Bug fix for !!/afk bug

When invoking the command with the option slash ```!!/afk```, It would ping the user twice immediately (going and returning from afk) because the input event didn't properly handle the optional slash. 

At some point we may want to extract this code into a helper method on the ```bot``` object.

Something like ```bot.getCommandNameFromMessage``` which would return a string for a valid command, or undefined for a message with an invalid command or no command.