UX pass

* Change default invitation and share app copy
* Add number of invited groups to metadata
* Label closed polls on User dashboard
* Do not include "Invitee did not vote" in metadata for closed polls

https://trello.com/c/HS5g3CW
Send an email to owner upon closing the event

https://trello.com/c/VDGLfOsQ
Extract vote related code into a module