Behat: Test for basic group elements

[Rebecca Blundell]

Automating manual test. Test from spreadsheet is below:

Pre req: Site Admin allowed to create groups

Displays Create group button, Group categories, Filter, Settings and Delete (to remove group permanently).
Click Accept button to join a group or Decline

1. Set up a new test called social/group_main.feature, with a @mainflow tag
2. Add 2 users and 2 groups as background steps.
 a. The first user should own GroupA and the second user should not be a member.
 b. The second user should own GroupB.
3. Admin logs in, turns on group categories.
3. UserA logs in, edits the group to add a category and invites UserB to join the group.
4. UserB logs in, goes the the Group page and should see the following:
- create group button
- group category
- Filter by label
In the GroupA row
- Accept
- Decline
In the GroupB row:
- Label
- Settings
- Delete

Note that if group category and invitations could be added in the background, this test would be shorter: https://bugs.launchpad.net/mahara/+bug/1892118