On incorrect command or the "help" command, send a help comment

[xmo-odoo]

Currently, on an incorrect bot command there's nothing really useful.

The bot should reply to that (or a "help" command) with a list of commands available to the user. This should probably be generated from Command (unrolled from enumerations), though not sure how to handle:

• parameterization
• context (e.g. close is only valid on fwport)
• descriptions (docstrings? No sure that works for enums)

Also update the wiki at last, I kinda forgot to do that still and it looks like the commands set hasn't been working too bad.