Jn/countdown

Countdown: Added countdown command.

* !countdown <time> <task>
* Countdown timer from 'n' (time in minutes set by user) to 0 for a task (text set by user).

Signed-off-by: Jakub Novak <jakub.novak@gmail.com>
It doesn't really need to be there, this creates a class variable with such a name and initalizes it. Unless we want to change them on setup time I believe this is pretty OK.

On the other hand putting it to setup could improve readability and I see your point about having setup everywhere. I'm not really sure if we should enforce that or not but I am fairly OK with it both ways.