www: Moved prefix form defs. to separate template

Moved the prefix form definition from the prefix add-template to a
separate template to prepare for re-use in an angularified prefix
edit-template. Prepared the controller & template by adding a variable
to the $scope to let the template know wherher it's used on an add- or
edit-page.

Refactored the code to keep state of whether the comment-field should be
visible or not.
www: 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.
www: 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.
www: 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
Made inherited tags field read-only

Made the inherited tags field read-only-ish with the workaround given in
https://github.com/mbenford/ngTagsInput/issues/241.

Also hid the iherited tags field in the prefix form when used on other
pages than the prefix edit page.
Merge pull request #634 from garberg/621-angularify_prefix_edit

Added AngularJS-version of prefix edit-page