Add script to shout to the channel

This script should:
- Be able to add a channel moderator (`channel` [m:m] `user`)
- Let the channel moderator request an `@channel` or `@here` shoutout through PM

Example PM to DojoBot:
`shout to #channel Hi all, I have an important message!`
-> `@channel: Hi all, I have an important message! - @chris`
