allow mod settings (non-tp settings) to be changed through chat

[red031000]

it would be convenient if mod settings (such as tweak's settings, and other mod settings) could be changed through chat by using the !set setting command or a variant of it

[samfundev]

It might be a good idea to take advantage of Tweak's settings editor, not sure. If we don't we should try to avoid code duplication with the existing settings commands.