Nextcloud 25 Hub 3 - Update

This updates Splash to work with Nextcloud Hub 3 aka Nextcloud 25.

What did we do this time?

• Advanced Theming - Removed specific Settings for users. They are now automatically integrated into the new Backgrounds!
• Added Transifex-Translations - Thanks @p-bo, @rakekniven, @nickvergessen and everyone who added translations!
• Remove support for PHP-Versions below 7.4

Known Issues:

• Blur is not beeing applied on dashbard