Store Pluggable Transport information in database

We currently save a bridge's ip address, orport, first seen timestamp, last seen timestamp, and distributor assignment in the database. Until now we've only needed this information, all other information is stored in-memory during runtime. With legacy/trac#13570 (closed) we need the bridge's PT information, as well.

Unfortunately the current schema is not ideal for this, and it will very likely change with a migration to a different database backend. As such the easiest solution right now is to mirror the current class relation of PluggableTranport -> Bridge by creating a table with columns: addr, port, transport, fingerprint (?). legacy/trac#9652 (moved) would help simply this relationship, in the future.