This commit also adds tests for the DB changes made in the previous
commit since we can now read the new field with the FetchChanInfos
method.
The commit following this one does the backfill migration.
This commit adds the full bbolt-backed client database as well as a set
of unit tests to assert that it exactly implements the same behavior as
the mock ClientDB.
A ClientChanSummary will be inserted for each channel registered with
the client, which for now will just track the sweep pkscript to use. In
the future, this will be extended with additional information to enable
the client to efficiently compute which historical states need to be
backed up under a given policy.
