Both `!help` and `!listcommand` are handled by the bot itself, so take
advantage of how the addons method calls work to implement both
`matrix_command` and `help_command` on `self`.
Add `help_command` to each currently enabled and functional addon
With the updated means of handling addons, update Custom Commands to
include the new logic and be functional.
addons/custom_commands.rb: Update for new addons logic
