New code for Team workflows

Added some code to make team workflows more extensible.  TeamWorkflows
implement SubitleWorkflows and also alter the pages in the team's
section like the dashboard and workflow settings page.

The plan from here is to:
  - Add extra TeamWorkflow subclasses to amara-enterprise.  This is
    what we will use for the collab-style teams
  - Add extra TeamWorkflow subclasses to our main repository.  I think
    we can create one for public teams, one for private teams, and
    maybe others.

Removed the is_moderated field from the team create form.  We weren't
using that value or displaying the widget to select it.
Wrong variable name (#1722)
Added workflow type to the TeamFactory (#1723)
Removed the Collaborators model

We are going to implement this with another app
Updated TeamFactory
Fixed a couple variable name issues (#1727, #1728)
Fixed constant name in TeamFactory
add workflow_type to team setup for tests.
change number from 42 to 43
Fix in data-url attribute in embedder on amara home page
Adjusted notes padding (#1713)

Took away padding on the very edge of the notes section.  Added it
inside the notes UL to make move the notes away from the scrollbar a
bit.
Run workflow setup code when creating teams
Fix for notes issue
Fixed field lookup
Couple of tweaks to workflow code.

These were made to make implementing the collab stuff easier.

- Made the PREFIX setting optional for urls.py in our optional apps.
- Allow subtitle workflows to define extra tabs for the video page.
- Couple convenience functions on TeamMember
- Added CSS style for tables that look nice (highly inspired by bootstrap).
Make the dashboard view a member of TeamWorkflow

We have a bunch of code that expects the dashboard page to be around
so it makes sense to force all TeamWorkflows to implement it.
Bump the amara-enterprise commit ID

Added code in update-integration.sh to also check out the correct
version of amara-enterprise
Fix for #1731
Don't run celery tasks locally in the dev enironment.
Merge branch 'staging' into team-workflows