Add a general flag to all commands (where feasible) to cause the bot to delete the command message and send its reply to that user by DM, so that PK usage doesn't clutter a channel.

E.g. pk;config timezone foo -din a channel would do the same action as usual, but delete that message and send its response to the user by DM rather than in channel.

• Allow this to be set as a default preference by user and/or server