Module: Groups plugin support

[JoryHogeveen]

Optionally support the Groups plugin if active.
See: https://github.com/itthinx/groups
Documentation: http://docs.itthinx.com/document/groups/

Can be improved with: itthinx/groups#59

VAA 1.7.2 - Initial PR: #59
Currently only supports features from the free version of Groups.

• groups_user_can & groups_group_can (though not really usefull when you are a super admin, use case possible with view combinations: View combinations #18)
• groups shortcodes
  • Custom shortcode implementation for groups_member & groups_non_member
• Page restrictions
  • I Replicate a 404 page when the selected user has no access to read. I use this since I can't hook into the posts_where filter from Groups.

Future

• More?