Add file header to test_parse_descriptors.py.
Add additional mocked bridge descriptors to test_parse_descriptors.py.
Move test_parse_descriptors.py SkipTest to setUp().
Add additional unittests for bridgedb.parse.descriptors module.
Add bridgedb.parse.descriptors module.

This module implements parsing bridge descriptors with Stem.

 * FIXES (partially) #9380.