More descriptive notifications for incoming messages.

This makes notifications more descriptive.  For a single incoming message, a notification might look like:

>**Vmail: Colin Sullivan**
>New Pull request received!

Or if the subject is long (limits arbitrarily defined in submitted changes):

>**Vmail: Henry Cowell**
>I am back from the dead!  You may remember me if you...

Or if there are multiple messages received:

>**Vmail: 3 new messages**
>Colin Sullivan: New Pull request rec...
>Henry Cowell: I am back from the dead!
>...