Implements a synchronous SMPP backend to send SMSes.

Based on smpplib.
Integration tests use SMPPSim, a testing SMSC written in Java. The
testing SMSC is integrated in the test suite so no need to launch
apart.
Implements a Redis-based backend to send SMSes.

Each request_sms may contain several recipients. The backend creates
a Hash per SMS, and a List per request_sms containing all the SMSes
keys. The request_sms List's key is appended to the List of
outgoing queues: 'oqs'. So we end up with:
 * One List 'oqs' that contains keys for
 * Lists per request_sms, that contains keys for
 * Hashes representing each SMS in a request_sms
App documentation is still pending.
Adds a demo site to play with redistore backend functionality
Merge branch 'master' of github.com:citylive/django-smsgateway into feature/redistore
Adds incoming SMS processing for redistore backend
Merge master (Gargoyle switches)
Merge Redistore backend

Also includes smpplib-based backend, but this is unused and can probably be
removed. The tests contain some Redis code too, so we shouldn't remove all of
it.