Python Version Check for Taskotron

[Miro Hrončok]

Hi.

I've prepared a check that makes sure packages do not require both 
Pythons (2 & 3), except explicitly listed packages. It is a common 
mistake when porting stuff to Python 3, that shebangs leave the 
dependency on Python 2 as well etc.

The review is here: https://phab.qadevel.cloud.fedoraproject.org/D948

I'm doing this for the first time, to please be patient with me.

Thanks,