feat: add option to change username

fix: rename subscriptions materialized view of the user too

remove materialized views from username change

fix: downcase username and limit username lenght (from routes/login.cr)

Users that changed their username to something like `User`, were unable
to login because the username is downcased on routes/login.cr

locales/en-US.json

@@ -522,6 +522,11 @@
     "carousel_slide": "Slide {{current}} of {{total}}",
     "carousel_skip": "Skip the Carousel",
     "carousel_go_to": "Go to slide `x`",
-		"footer_contact_url": "Contact the Administrator"
-
+    "footer_contact_url": "Contact the Administrator",
+    "new_username": "New username",
+    "change_username": "Change username",
+    "username_required_field": "Username is a required field",
+    "username_empty": "Username cannot be empty",
+    "username_is_the_same": "This is your username, use another one",
+    "username_taken": "Username is already taken, use another one"
 }