groupmenu module updated to a usable state

[ericras]

I didn't find the current state of https://www.drupal.org/project/og_menu usable. Having a working implementation of this is a blocker for OG use since we want/need a menu for every group.

This might be a pretty big task to start working on that module but we might not have a choice. One of the devs claims to be using it in production but I can't get it working.

[ericras]

Switching to Group - https://www.drupal.org/project/groupmenu

[ericras]

For .gitignore:

# Ignore Group menus by ignoring all menus then adding back in the core ones with !
config/sync/system.menu.*
!config/sync/system.menu.account.yml
!config/sync/system.menu.admin.yml
!config/sync/system.menu.footer.yml
!config/sync/system.menu.main.yml
!config/sync/system.menu.tools.yml