Added a "pin" button on models view (scroll up/down models view with is really annoying)

Using the Models tab with a lot of scopes is really annoying. To view some scopes, I needed to scroll down the tree on the left, and scroll up to view the model, then scroll down again, and so on... Also, I removed that weird grayed background on scope tree. With more than 3 or 4 scope levels, the links become unreadable.