Support for Verizon VTEXT.COM messages

Hello,

I had some bounce messages from US mobile carrier Verizon's VTEXT.COM Email-to-SMS gateway services which BounceHammer could not parse.  I have added in some rudimentary support for them.

I did not know how to use these to parse without adding them to the list of default MTAs, so I have included those changes too.  Maybe there is a better way to do this.

Thanks,

------Scott.