Update drag and drop behaviour
Update drag and drop behaviour

Now, instead of the top 50% being used for sorting project folders and
the bottom 50% for moving the actual files, the middle 40% is used for
moving the actual files, and the top & bottom 30% is used for sorting
project folders.

samu/tree-view,atom/tree-view,jarig/tree-view,learn-co/learn-ide-tree