env paths - sort paths by env name

This commit is provide a common behavior for the ordering
of the environment paths.

The initial issue observed was similar to:
 - paths:
   - dev, test, prod
   - dev-2, test-2

 - When a user would go to Changesets page, they would
   see the first path (dev, test, prod); however, the
   'next environment' would be dev-2.  The reason being
   the path ordering listed was sorted, but the determination
   of next environment used the paths unsorted.  This
   could result in the user creating a changeset and
   the content being promoted to dev-2; however, the user
   might assume it is going to dev, since that is the env
   path being displayed.

This change provides for a consistent behavior in the
various places where an env (or promotion) path is involved,
such as:
 - changesets
 - changeset history
 - activation keys
 - systems
 - organization
 ...
Merge pull request #1665 from bbuckingham/sort_promotion_paths

env paths - sort paths by env name