Add backtraces to errors (#1498)

Error handling has been reworked to always go through the new `error_template`,
`error_json` and `error_atom` macros.
They all accept a status code followed by a string message or an exception
object. `error_json` accepts a hash with additional fields as third argument.

If the second argument is an exception a backtrace will be printed, if it is a
string only the string is printed. Since up till now only the exception message
was printed a new `InfoException` class was added for situations where no
backtrace is intended but a string cannot be used.

`error_template` with a string message automatically localizes the message.
Missing error translations have been collected in https://github.com/iv-org/invidious/issues/1497
`error_json` with a string message does not localize the message. This is the
same as previous behavior. If translations are desired for `error_json` they
can be added easily but those error messages have not been collected yet.

Uncaught exceptions previously only printed a generic message ("Looks like
you've found a bug in Invidious. [...]"). They still print that message
but now also include a backtrace.

src/invidious/channels.cr

@@ -208,7 +208,7 @@ def fetch_channel(ucid, db, pull_all_videos = true, locale = nil)
 
   author = rss.xpath_node(%q(//feed/title))
   if !author
-    raise translate(locale, "Deleted or invalid channel")
+    raise InfoException.new("Deleted or invalid channel")
   end
   author = author.content
 
@@ -226,13 +226,14 @@ def fetch_channel(ucid, db, pull_all_videos = true, locale = nil)
   videos = [] of SearchVideo
   begin
     initial_data = JSON.parse(response.body).as_a.find &.["response"]?
-    raise "Could not extract JSON" if !initial_data
+    raise InfoException.new("Could not extract channel JSON") if !initial_data
     videos = extract_videos(initial_data.as_h, author, ucid)
   rescue ex
     if response.body.includes?("To continue with your YouTube experience, please fill out the form below.") ||
        response.body.includes?("https://www.google.com/sorry/index")
-      raise "Could not extract channel info. Instance is likely blocked."
+      raise InfoException.new("Could not extract channel info. Instance is likely blocked.")
     end
+    raise ex
   end
 
   rss.xpath_nodes("//feed/entry").each do |entry|
@@ -287,7 +288,7 @@ def fetch_channel(ucid, db, pull_all_videos = true, locale = nil)
     loop do
       response = get_channel_videos_response(ucid, page, auto_generated: auto_generated)
       initial_data = JSON.parse(response.body).as_a.find &.["response"]?
-      raise "Could not extract JSON" if !initial_data
+      raise InfoException.new("Could not extract channel JSON") if !initial_data
       videos = extract_videos(initial_data.as_h, author, ucid)
 
       count = videos.size
@@ -507,8 +508,7 @@ def fetch_channel_community(ucid, continuation, locale, format, thin_mode)
   end
 
   if response.status_code != 200
-    error_message = translate(locale, "This channel does not exist.")
-    raise error_message
+    raise InfoException.new("This channel does not exist.")
   end
 
   ucid = response.body.match(/https:\/\/www.youtube.com\/channel\/(?<ucid>UC[a-zA-Z0-9_-]{22})/).not_nil!["ucid"]
@@ -518,7 +518,7 @@ def fetch_channel_community(ucid, continuation, locale, format, thin_mode)
     body = initial_data["contents"]?.try &.["twoColumnBrowseResultsRenderer"]["tabs"].as_a.select { |tab| tab["tabRenderer"]?.try &.["selected"].as_bool.== true }[0]?
 
     if !body
-      raise "Could not extract community tab."
+      raise InfoException.new("Could not extract community tab.")
     end
 
     body = body["tabRenderer"]["content"]["sectionListRenderer"]["contents"][0]["itemSectionRenderer"]
@@ -540,7 +540,7 @@ def fetch_channel_community(ucid, continuation, locale, format, thin_mode)
            body["response"]["continuationContents"]["backstageCommentsContinuation"]?
 
     if !body
-      raise "Could not extract continuation."
+      raise InfoException.new("Could not extract continuation.")
     end
   end
 
@@ -551,7 +551,7 @@ def fetch_channel_community(ucid, continuation, locale, format, thin_mode)
     error_message = (message["text"]["simpleText"]? ||
                      message["text"]["runs"]?.try &.[0]?.try &.["text"]?)
       .try &.as_s || ""
-    raise error_message
+    raise InfoException.new(error_message)
   end
 
   response = JSON.build do |json|
@@ -786,21 +786,19 @@ def get_about_info(ucid, locale)
   end
 
   if result.status_code != 200
-    error_message = translate(locale, "This channel does not exist.")
-    raise error_message
+    raise InfoException.new("This channel does not exist.")
   end
 
   about = XML.parse_html(result.body)
   if about.xpath_node(%q(//div[contains(@class, "channel-empty-message")]))
-    error_message = translate(locale, "This channel does not exist.")
-    raise error_message
+    raise InfoException.new("This channel does not exist.")
   end
 
   initdata = extract_initial_data(result.body)
   if initdata.empty?
     error_message = about.xpath_node(%q(//div[@class="yt-alert-content"])).try &.content.strip
     error_message ||= translate(locale, "Could not get channel info.")
-    raise error_message
+    raise InfoException.new(error_message)
   end
 
   author = about.xpath_node(%q(//meta[@name="title"])).not_nil!["content"]