Stop requiring a refreshToken for inviters.

The immediate reason to do this is to avoid having to query the
refresh token of invite@getlantern.org every time we process an
invite from inviteme@getlantern.org.

In any event, we no longer need users to send us tokens on invite,
since the pool of users for which we're running fallback proxies
is more or less fixed.  Then again, I didn't want to remove that
logic altogether from controller and client because that's not
necessary for this particular feature.

What I did was stop accepting inviters with no fallbackProxyUserId,
since we should no longer have those in LanternUsers and if this
ever happens again we really want to catch it ASAP.
Enqueue invites to everyone that sends me mail.
Ignore emails matching certain regexes.
Extract original sender from forwarded emails.

While the controller will listen for new requests at
invite@<controller-id>.appspotmail.com, forwarded emails should go
to forward@<controller-id>.appspotmail.com, so we know to treat
them differently.

This works for single e-mails forwarded from one's personal inbox.
Unfortunately, Google Groups strips the original sender's address
if you forward from the mailing list interface.  Also, digest mode
is not supported yet.
More aggressive, thorough and robust compiling of emails.

Handles abridged and digest emails.  I imagine it could cause
false positives, but little harm is caused if the invitee just
ignores the invite mail.
Take Dao creation out of loop.
Make email regex accept emails not surrounded by angled brackets.

This requires our regex to be more robust, although it will never
be totally immune to false positives or to fail to recognize valid
(if weird) email addresses.
Add some email filters.
Remove unused imports.
Simplify email address matching regex, make it more robust, unit test.

The unnecessary use of delimiters in the old regex was breaking some
cases that, while not relevant for our purposes, were more quickly
fixed than documented.
Authorize and send mail-triggered invites if invites are not paused.

This incurs a minor duplication, but finding a good place to
centralize this operation would involve refactoring that is not
warranted at this moment.
Merge pull request #51 from getlantern/inviteme

Enqueue invites to senders of mail to this controller