Track opens of sent emails.
Adding bumped version
Ameliorate the damage of concurrent modification exceptions.

Fix NullPointerException when trying to change invite status. We'll
get a RuntimeException right after that anyway, but at least that
is more informative.

Do statistical incrementing of invites assigned to a fallback proxy
to remove some pressure from that.  In any event, avoid crashing
because of this, since invites fail to get processed in this case.
Adding bumped version
Stop making the inviter's fallbackProxyUserId an ancestor of Invites.

This was making all transactions involving status changes to invites
made by users with a given fallbackProxyUserId compete with each
other unnecessarily.
Fix: find old invites.
Adding bumped version
Merge pull request #53 from getlantern/orphan-invites

Stop making the inviter's fallbackProxyUserId an ancestor of Invites.
Adding bumped version
Add a bogus parent key to Invite.

This is so objectify can load old invites.
Adding bumped version
Remove email endpoint.
Adding bumped version
Adding bumped version
Merged from master