App sharing modals allow for sharing with an indiviudal group

* Remove abaility for user to remind multiple groups
* This setup is closer to the sharing capability allowed by the Yammer embed widget
* Remove unused Yammer api methods
* Remove logic that tracks if a user has shared the app post vote since the modal is now delayed until 45 seconds post vote

https://trello.com/c/BevzcF5T
https://trello.com/c/5aFF2lBs