Dirty tracking. Delete code we're moving.

- Dirty tracking
- Delete file-browsing code from ramp-editor-main,
  since we're moving it into ramp-editor-file-browser
- Set up two-way binding between $scope.file.contents
  and editor value
Select first first on initial load
Add saving
Meta-s saves
Warn before leaving if unsaved changes
Disallow duplicate filenames (case-insensitive)