* Prepare Mastodon for zeitwerk autoloader (Rails 6)
Add inflections and rename/move a few classes.
In particular, app/lib/exceptions.rb and app/lib/sanitize_config.rb
were manually loaded while still in autoload paths.
* Add inflection for Url → URL
* Fix#2119 - Whenever about to send a HTTP request, normalize the URI
* Add test for IDN request in FetchLinkCardService
* Perform IDN normalization on domains before they are stored in the DB
application website validation, don't link to app website if website isn't set,
also comment out animated boost icon from #464 until it's consistent with non-animated version
Claire