Private commands and responses

[gilith1]

Accept commands over private messages, and respond over private messages too. This would limit the amount of spam on #auction-bot-sandbox.

Some commands need visibility and should not work over private messages:

• $bid - for obvious reasons
• $whohas - ? to be decided. If someone's peeking at others' inventories, maybe it's better to keep it visible

All the commands should still remain usable on channels too. General rules: command over priv msg -> response over priv msg, command on the channel -> response on the same channel