Added AngularJS-version of prefix edit-page

The next step on our path towards porting the NIPAP web UI to AngularJS
has been taken, with the angulatification of the prefix edit-page.
Added a PrefixAddController, a template and routes to the new controller
& template.

Statistics needs to be added before the page can be considered in
feature parity with the old prefix edit-page.
Added statistics to ng-prefix edit-page

Added statistics to the AngularJS-version of the prefix edit page. Did
it in a quite 'hacky' way to keep up the steam, it should be done in a
more AngularJS-ish way in the future.
Link to ng-edit prefix-page in prefix list

Changed the 'Edit prefix' link in the prefix list popup menu to the
AngularJS version of the edit prefix-page.

Fixes #621