finished

* redraw before rendering (workaround for bug)
* play the first file once on init (before first file was assumed to be first file in demo_config.py which often isnt the case)

Beware: in mocap/__init__.py there was a very long bl_label (> 100 chars), which was troncated in UI (at least, _update_msg.py produced a troncated msgid for it). That should be avoided, imho!

Plus a few styling enhancements.

[[Split portion of a mixed commit.]]

* 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

- added next/previous buttons so you can skip demos.

work in progress addon: demo mode, use for easy setup for looping over blend files, rendering, playing, switching screens.