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/routes/watch.cr

@@ -12,9 +12,7 @@ class Invidious::Routes::Watch < Invidious::Routes::BaseRoute
       id = env.params.query["v"]
 
       if env.params.query["v"].empty?
-        error_message = "Invalid parameters."
-        env.response.status_code = 400
-        return templated "error"
+        return error_template(400, "Invalid parameters.")
       end
 
       if id.size > 11
@@ -56,10 +54,8 @@ class Invidious::Routes::Watch < Invidious::Routes::BaseRoute
     rescue ex : VideoRedirect
       return env.redirect env.request.resource.gsub(id, ex.video_id)
     rescue ex
-      error_message = ex.message
-      env.response.status_code = 500
       logger.puts("#{id} : #{ex.message}")
-      return templated "error"
+      return error_template(500, ex)
     end
 
     if preferences.annotations_subscribed &&