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
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
Merge remote-tracking branch 'mozilla/master' into curatedgroups

Conflicts:
	mozillians/settings/base.py
	mozillians/templates/phonebook/edit_profile.html
[Bug 936569] Curated Groups: Allow users to create/manage groups
[Bug 936569] merge curatedgroups branch into master, thanks to @dpoirier and @wbowling

Bug 951840, bug 936570, bug 937673, bug 938184, bug 938674, bug 938680,
bug 938695, bug 938723, bug 939127, bug 947271, bug 948491, bug 948640,
and bug 951515 are fixed by this patch.