Move contact's preferred service out of Memory

[seanhealy]

Currently the preferred service (SMS or iMessage) is stored in memory. This should be moved to a database. Thinking SQLite would work nicely until there is a better client server break (#2) where moving to a more scaleable db would make more sense.

Likely would be good to use https://github.com/typeorm/typeorm or something like it to be safer with any db moves in the future.