gkeys/config.py: Remove self.configparser.add_section('DEFAULT') from read_config()
gkeys: New checks.py and Key_checks class

Move GkeysGPG.check_keys() code to the KeyChecks.validity_checks()
gkeys/checks.py: Use passed in logger instance
gkeys/actions.py: Update checkkey() to use the SeedHandler.load_category()
gkeys/check.py: Remove invalid long_keyid == keyid[2:] check for SUB key types

This caused it to not detect perform subkey checks because they subkey id is never
the same as the primary keyid being checked.
gkeys/check.py: Add sign check for PUB type keys
gkeys: stub cleanseed, cleankey options
gkeys/actions.py: Move ssl-fetch import to action function it is used

This reduces the import load to only be for the function it is used.
It also removes the import on a system that does not have all the dependencies installed.