DDF-669 DDF-670 DDF-682

DDF-670 - Restyles the admin application modules.  Setup initial application selection page for Jeren and Sam's work.

DDF-669 - Created Feature management backend API and Feature UI via
config plugin.

DDF-682 Created configuration plugin API framework.  Adjusted
configuration UI to work within a Configuration Plugin.
We will be addressing this outside of this PR.  https://tools.codice.org/jira/browse/DDF-706