GUI.py: Destroy subreddit widgets
GUI.py: Destroy subreddit widgets

Hides the subreddit textbox and label when
Reddit checkbutton is unclicked.

Fixes #211

nemaniarjun/UIP,Aniq55/UIP,DarkSouL11/UIP,Aniq55/UIP,VK10/UIP,nemaniarjun/UIP,VK10/UIP,NIT-dgp/UIP,NIT-dgp/UIP,hackrush01/UIP