content views - ui - create/update composite view definition

This is an initial commit to allow a user to create
a composite view definition as well as update it's contents.

There will be additional commits for handling things like
permissions within the views and for usability.
content views - ui - component views may not have same repo

When a user creates or updates a composite definition
which consists of one or more component views, they
should not be allowed to select content views
having one or more repositories in common.  This
commit adds logic to the UI so that the user may only
select views with unique repositories.  Once a
view is selected (checked) any other views with overlapping
repos will be disabled.  (When the view is unselected,
those views will be re-enabled.)

e.g. Assume:
view1 has repoA
view2 has repoB
view3 has repoA & repoB

User may create composite definitions with the following
combinations of these views:
- view1 & view2
- view3
Merge pull request #1402 from bbuckingham/fork_content_views_composite

content views - ui - initial support for create/update composite definition