Blender Git Loki

Annoyance fix:

Using scrollwheel on properties window halted when it was over
a list-button. Now it disables handling wheel events when you use
scrollwheel outside of lists first.

Implementation note: UI event handlers have priority over other
keymaps. That's OK. In this case it's simple conflict, for which
no design solution exists... wouldn't know how to do this nicer!
Code is nice local and can be improved when we look into other
conflicts...