Create a Key-Value database system for simple/flat datatypes in BridgeDB

BridgeDB will likely need some rather high-level code for interacting with Redis through Twisted in order to complete Section 2 of proposal #226.

We'll probably want to start with storing the (emailAddress,timestamp) pairs for the bridgedb.Storage.getEmailTime and bridgedb.Storage.getWarnedEmail inside Redis. Other simple datatypes which can be stored in Redis should eventually get listed here (and eventually in bridgedb-spec.txt.