title: Limiting commands to certain channels
body: <p>I'm trying to build a bot with Commando, but I can't figure out a way to make the bot ignore commands (or better, delete and ignore) commands that are not sent in a defined channel. For example, if you don't send the command in #botchat the message gets deleted.</p>
  
  <p>I know that I could deny the read permission to the bot in the other channels, but I have other modules running, and they require reading channels.</p>
  
  <p>I could add a check at the beginning of every run function, but this won't affect the default commands.</p>
  
  <p>Is there a way to write a check function that is run for every command before the actual run function begins? (Maybe using the Command class?)</p>