Deprecate bridgedb.Bridges.is_valid_fingerprint().

 * MOVE bridgedb.Bridges.is_valid_fingerprint() to
   bridgedb.test.deprecated module for regression testing.
 * REMOVE bridgedb.Bridges.toHex().
 * REMOVE bridgedb.Bridges.fromHex().
 * REMOVE bridgedb.Bridges.HEX_FP_LEN.
 * ADD bridgedb.parse.fingerprint module. This now contain equivalent
   functionality to the above removed/moved objects.
 * ADD monkeypatcher code for all the above removed/moved code to
   bridgedb.test.test_Tests suite for regression testing.