content views - update authorization to handle headpin mode

This change is to ensure an authorization failure does not
occur during headpin mode.
content views - include all views in select on systems, akeys...

This commit is to remove the usage of 'non_default' scope
when retrieving a list of content views.  This means
that the list returned will all in the environment.
This can be useful on the 'select' input that is used
on Systems and Activation Keys.
content views - enable/disable buttons on env content view selector

This commit contains changes to enable/disable the save/cancel
buttons associated with the 'environment / content view' selector.

E.g.
buttons initially disabled
user changes env or view, buttons enabled
user save change, buttons disabled
user cancels change, buttons disabled
path selector - update behavior of select_mode=single

This commit changes the behavior of the 'single' select mode,
where a user can only have 1 environment selected at a time.

Example:
- assume dev, test, prod exist
- dev is selected

Scenario: User wants to select 'test'

Before the change:
- unselect dev and then select test

After the change
- select test (and dev is automatically unselected)

After the change:
Merge pull request #2346 from bbuckingham/delete-legacy-promotion

delete-legacy-promotion - a few commits to improve behavior