Debug command to manage the 'Playing' status

[Silari]

New debug command that sets the Playing status and ensure it's set again when the bot connects. Currently it's possible to use eval to set that status, but this is lost if the bot reconnects to discord and fires the 'on_reconnect' event.

I should instead make a command that sets a variable. If the variable isn't set, use the default status. If it has been set, use the set message. This would mean making a small function to check the value and call change_presence.