Q&A commands

[sustained]

Rationale

It could potentially help Q&As to go more smoothly if we had some commands to aid the process.

Usage

Copied from Elfayer's original issue.

• !start-qa <user1> <user2> ... - Would provide writing right on #q-and-a channel, also write an opening message welcoming users as guests tagged in args. (Could also provide users q&a guest rights for coloring.
• !end-qa - Would turn off writing right on #q-and-a channel, also write a closing message.
• q-and-a-management - (From Reactiflux) Only active during Q&A. Make sure there is no more than 3 questions ongoing, otherwise warn message. (Have to determine the counting)