Tree find widget should not render over the tree contents

[joaomoreno]

[benibenj]

The Tree Find Widget now gets enough space at the top of the tree to make sure to not render above the tree contents

[benibenj]

Currently the find widget is still draggable. This was introduced to allow to see the first element in the tree. This is now possible with the empty space at the top so removing it would make sense. The only benefit from keeping it currently would be to allow looking at the first sticky scroll element.