Refactor Applications controllers so they better represent the 3 context

Refactor, clean up and extract common logic from the applications controllers. There are 3 different contexts for actions: index, new and create and some cleanup is required now that we're remaking the forms with Patternfly-react.

• p/admin/applications (Audience context)
• buyers/account/:id/applications (Account context)
• apiconfig/services/:id/applications (Product context)