make form groups reorderable

Summary:
make form groups reorderable on the frontend, reuse the same ordering code from attributes, fixes T838

delinting

Test Plan: try adding and reordering form groups and attributes

Reviewers: rjmackay, shadowhand

Reviewed By: shadowhand

Subscribers: srutto

Maniphest Tasks: T838

Differential Revision: https://phabricator.ushahidi.com/D437