Tweak left-key behavior on Trees.
Tweak left-key behavior on Trees.

Instead of collapsing and changing selection to the parent in one key press,
do the collapse on one key press and change the selection on the second.

This is more inline with most desktop UIs.

Anaminus/gxui,xinhuang327/gxui,henrikhodne/gxui,mzgnr/gxui,insionng/gxui,Drahoslav7/gxui,rnubel/gxui,MeGaPk/gxui,henrylee2cn/gxui,google/gxui,pombredanne/gxui,ylong/gxui,jmptrader/gxui,treejames/gxui,abadojack/gxui,cainiaocome/gxui,leelib/gxui,CodyGuo/gxui,UIKit0/gxui