Add per-channel regex filtering

This pull request adds the enableregex, disableregex, resetregex, and regexstatus. It makes it so that the bot won't match any regex values unless the 'regex status' of that channel is enabled.

By default, the default channel regex enabled status is true, but that can be changed. If the default value is true, unless .disableregex is used, regex is enabled in all channels. If the default value is false, a bot admin must use .enableregex before regex is enabled in any channel.