ircbot.py: support for custom config file

Introduce command line argument parsing and let the first
usage be for the support of using a custom config file for the bot.

Signed-off-by: Petter Mabäcker <petter@technux.se>
redmine_interface.py: Catch unsupported commands

When an unsupported command is used, return a list of strings
with hints to the user.

[TechnuxBot #11]

Signed-off-by: Petter Mabäcker <petter@technux.se>