make addons blender versions consistent

finished

* You only have to do layout.prop if you want 1 property, no need for row then!
* Use col, row, sub as variable names, not colsub, rowsub, row2 etc please.
* Povray Addon: Still used a lot of splits, you need no split when you only have 1 column! 

- remove/comment unused variables
- remove unused imports
- fixed some bugs using incorrect variables

Thanks to Yousan Noriyuki.