add scroll to top button
fix kissmanga filename regex
fix batoto bug when viewing webtoons

For whatever reason, batoto seems to be nice to webtoons: a chapter's
pages are displayed all at once, unlike others where you can only view
one page at a time.

This update adapts the batoto handler to take that into account. Now
webtoons will load faster because all pages are fetched at once.
Remove "credentials mismatch" alert

It's just annoying. Also, remove the "token" item from localStorage so
the app won't try validating again when it's refreshed.