Auto-register for email gateway if necessary
Auto-register for email gateway if necessary

If attempting to send to an email address from an unregistered
account, auto-send registration to mailchuck.
Use label if possible, otherwise random 12 characater address

Fixes #131

mailchuck/PyBitmessage,mailchuck/PyBitmessage,mailchuck/PyBitmessage,mailchuck/PyBitmessage