Add `correct` channel setting to allow regex string replacements

[empus]

• Add correct channel setting to allow regex string replacements.
• Requires the trakka plugin to be loaded (but not necessarily enabled in the channel)

Enable string correction responses:

@Empus | y modchan correct on
 @yolk | done.

Replace soccer with football:

@Empus | This soccer World Cup has been a wild ride.
@Empus | s/soccer/football/
 @yolk | correction, <Empus> This football World Cup has been a wild ride.

Remove the text don't:

@MrBob | My wife seems upset with me... I don't know why. 
@Elmo  | uh oh!
@Empus | s/don't //
 @yolk | correction, <MrBob> My wife seems upset with me... I know why.
@Empus | haha.  Seems more likely :>

[empus]

Done