Blacklist certain attachment regexs

[andrewferrier]

e.g.

.*email_oyster_logo.*

Needs to be configurable.

Use https://docs.python.org/3/library/configparser.html to support configuration files (align them with argparse options?). See https://docs.python.org/3/library/argparse.html#argparse.ArgumentParser.parse_known_args and http://stackoverflow.com/a/5826167/27641