Make it more obvious when a form is saved

Summary: display an alertify success notice when form models are saved, fixes T905

Test Plan: Try adding new fields to forms, reordering them, editing, and deleting them.

Reviewers: rjmackay, vladimir, shadowhand

Reviewed By: shadowhand

Subscribers: srutto

Maniphest Tasks: T905

Differential Revision: https://phabricator.ushahidi.com/D433