Bug 937673 - Modify groups model to allow user-created curated groups

* Add flags for functional area, members_can_leave, visible
* Get rid of system, auto_complete, and related fields
Bug 938184 - Don't allow creating groups while editing user profile

Part of the changes for curated groups is that groups will only be
creatable from the groups list page, so only allow people editing
their profiles to select groups that already exist.

The tag-it library that was being used to implement the groups
selection could not easily be configured or modified to prevent
users from selecting non-existent items, so the groups field
was changed to use django-selectable. Styling was added to make
the django-selectable field look like the current tag-it fields,
which are still being used for e.g. skills and languages.
Remove some unused code from groups/forms.py
[Fix Bug 938674] Added Create Group button the Groups list page (+2 squashed commits)

only translating the words in the create group button

[Fix Bug 938674] Added Create Group button the Groups list page
merging Bug 937673 - Modify groups model to allow user-created curated groups
merging: Bug 938184 - Don't allow creating groups while editing user profile

Part of the changes for curated groups is that groups will only be
creatable from the groups list page, so only allow people editing
their profiles to select groups that already exist.

The tag-it library that was being used to implement the groups
selection could not easily be configured or modified to prevent
users from selecting non-existent items, so the groups field
was changed to use django-selectable. Styling was added to make
the django-selectable field look like the current tag-it fields,
which are still being used for e.g. skills and languages.
merging:  Remove some unused code from groups/forms.py
Merge remote-tracking branch 'upstream/pr/726' into curatedgroups-merge
[Bug 940941] Show helpful message if searching logged out
Merge pull request #735 from jschneier/issue-940941

[Bug 940941] Show helpful message if searching logged out.
Update migrations
Merge pull request #1 from dpoirier/curatedgroups-merge

Update migrations for curatedgroups-merge
Fix group editing
Merge pull request #2 from dpoirier/fix-group-editing

Fix group editing
Merge branch 'curatedgroups-merge' into curatedgroups