Python actions

Python actions are imported from action.d config folder, which have .py
file extension. This imports and creates an instance of the Action class
(Action can be a variable that points to a class of another name).
fail2ban.server.action.ActionBase is a base class which can be inherited
from or as a minimum has a subclass hook which is used to ensure any
imported actions implements the methods required.
All calls to the execAction are also wrapped in a try except such that
any errors won't cripple the jail.
Action is renamed CommandAction, to clearly distinguish it from other
actions.

Include is an example smtp.py python action for sending emails via smtp. (WIP)