Handle Connection Errors in Developers App Keys Page (bug 926630)

- Move the external call from the template to the view
- If a connection to solitude fails or raises non 200 catch the exception
- Log the problem
- Display a message to the user
- Added an appropriate test
Merge pull request #1742 from JaredKerim-Mozilla/926630

Handle Connection Errors in Developers App Keys Page (bug 926630)