fix keyboard navigation in objects dialog. ref inbox#10033
Fixed the keyboard navigation in the objects and layers dialog as requested in inbox#10033
Changes:
- Up and Down arrows now move the selection up and down
- right and left arrows expand and collapse the node (rather than shift+right or left)
- Previously shift+up and down moved an item up or down, I changed this to multi-select to match with the mouse bindings
- ctrl+up and down now move items up or down
Multi-select is a little unintuitive, normally if you press shift+up the selection grows up then if you press down the selection would shrink. The way I have it implemented shift+up grows the selection up, then shift+down grows the selection down. I don't think it's a big deal though.
I don't do much c++, so open to any recommendations.