Blender Git Loki

Make uiLists placed in popups usable

It's still not completely working - there are still some glitches - but far better than before.
To make buttons of the uiList work, you have to add a 'check' callback to the operator that invokes the menu. Only if it returns True, the uiList gets refreshed. To avoid this we have to make the region refresh tagging in the entire button handling a bit smarter.

Changes I had to do:
* Call uiList handling from menu/popup handling if needed.
* Make uiList handling use special popup refresh tag if placed in menu.
* Allow popups invoked from py operator to tag for refresh by using operator 'check' callback.
* Tag popup for refresh when resizing uiList.

Mostly fixes T48612.