Preserve tree-view state in Outline panel after switching tabs

[mindplay-dk]

When switching between tabs, the Outline panel loses it's state - all of the tree nodes collapse down to the root, and have to be expanded again.

[jbaron]

Workaround is that now by default tree nodes are open (till a sensible number). Not yet remembering their state, but at least normally you don't have to reopen them every time.