Add proper multi guild (discord server) support

[optimumtact]

DB should be stored in a map per discord server.

Add in a layer for
TGDB.get_api_with_context(ctx) that returns a TGapi object that is prepopulated with
the message context (from the bot) and the db server for that discord.

The api layer should host all TGDB convenience functions that wrap the tables, and allow calling SQLalchemy direct queries against the db.