Don't Load Tree When It's Hidden?

[Norn]

When the Tree is hidden, it shouldn't continue loading and updating in the background. This can noticeably slow things down when there are tens of thousands of folders.
It would be better to temporarily enable "Lock Tree (#488)" while the Tree is hidden, and resume normal loading when it's shown again.

[admin]

Under the hood, the tree is the backbone for many functions. It has to be in a valid state. The auto-locking idea sounds good though. Needs thinking and testing. Later.