Ide fixes

Some fixes for the IDE. Including:
* Increasing standard UIVScrollBar scroll speed to make it feel more natural,
* Fixing that if you clicked twice on an asset in the AssetBrowser, it would be viually deselected. 
* Adding that you now can choose assets by doubleclicking them in the asset browser.
* Adding that you now can toggle collapsed by doublecklicking an UITree node with children.
* Adding that examples get automatically opened when doubleclicking them (you don't have to always use "OK")

I think I might add some more - just wanted to create the PR for @ivansafrin, that he knows what I'm doing :)

Fixes: #590