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.
Not sure if this is described in any conventions (DDF or otherwise). @shaundmorris  might know, but for consistency with the rest of the code (including this file) I think this should be at a warn level:
```java
logger.warn("There was an error while trying to access the application", e);
```
It looks like you're using warn for other exceptions so it would be good to have them all the same. This might be something different and more severe though, so if it is just let me know :)