Aliases for /bc /ac, ban bug fix, /help update

-/idle is a new alias for /blockchallenges (familiar to PO users) and /back is its counterpart, alias for /allowchallenges.
-/help has been updated to show challenges commands and forcerename and alts are now listed under drivers commands.
-Offline users can now be banned with a reason.
-Added /um as alias for /unmute
-Adding FAQ link to !intro
-Typo fixed
Merge pull request #141 from Joimer/patch-4

Aliases for /bc /ac, ban bug fix, /help update