Quick item tree: Auto expand slighly smarter.

Now it only auto-expands items with less than 5 siblings (including
the item itself).
Quick inspector: Fix assert on exit.

QuickItemModel::updateItem would hit an assert when item->window() was
0. But on exit, this is a valid scenario. Now in this case it will
just return from that function.
Add all 4 custom render modes to quick inspector.

These are
- clip
- overdraw
- batches
- changes