Issue #3192493 by sjoerdvandervis: Change logic; remove RouteSubscriber and add about URL to the variables sent towards the template file. Then, we'll just print this about url in this specific block

This removes the styling for the sky theme for the group join button.
The `transform: uppercase` was removed from Open Social quite some time
ago for a11y reasons and should not be re-introduced. Additionally the
`.btn-block` class exists for full width blocks. Using this per button
instead of forcing it from outside allows the dropdown for the
accept/join button that is desired.

The dropdown styling is also applied to the old flavour.

Issue #3119327 by ronaldtebrake: Ensure the statistics block shows the same markup for the accept decline button in sky as the hero in socialblue

Issue #3119327 by ronaldtebrake: make sure the group invites tab is only visible on correct places and not on every user.route

Issue #3119327 by ronaldtebrake: ensure accept and decline also works on invite and remove the groups tab when not needed

Issue #3083877 by agami4: Update group page, add styles and script for secondary nav on the profile and group pages