Instead of running stand-alone, this application is now a set of Rack
middleware that get injected to sgx-catapult.  That means sgx-catapult
is now a hard dependency (and is included as a submodule so we can
easily manage the version of that dependency, etc).  sgx-catapult's
Gemfile is included in our own (though we can have extra stuff if we
need it).

Basically, *instead* of running sgx-catapult at all, a user of this
version of fwdnum runs only this instead, and points catapult callbacks
for both messaging and voice to this one instance that will be augmented
to handle both kinds of data coming in.

Additionally, everything has been refactored to not use blocking IO,
since changes were large enough that I just went ahead and did that at
the same time.

No behaviour should change at this point, but this will make future work
(such as voicemail and ad-hoc commands to configure fwdcalls) much
easier.