Feature: Redesign admin page

[HeyItsBATMAN]

We cleaned up and redesigned the administration page, where page admins can change user roles and can see an overview of all user-generated content.

The page has been redesigned to make changing user roles easier by allowing to filter through the user roles with buttons as well as an alphabetically sorted & autocompleted search input.

Changes:

• Button Group allows filtering by role
• Search input with autocomplete is now alphabetically sorted and also shows the user mail next to the username (and uses the selected role from the button group)
• The user information has been condensed to a table
• Promoting (changing a user role to uploader) and demoting (changing a user role to user) is now context-dependent, so the most relevant choice is the one that will be shown.
• User-generated content is now hidden in an expansion panel to reduce visual clutter

Before:

After: