Extend BlockedBridges table

BridgeDB has a (currently unused) table in its SQLite database that captures where a bridge is blocked. We are going to use this table as part of our work on legacy/trac#32740 (moved). It currently has the following fields:

• ID (primary key)
• hex_key (fingerprint)
• blocking_country (country code)

A fingerprint can relate to a bridge's OR port or any of its pluggable transports but these endpoints can be blocked independently. To remove this ambiguity, we should add additional fields for a bridge's IP address, port, and perhaps for an autonomous system because blocking isn't always uniform across a country.