Drag and drop bugs around readonly folders

[jameskerr]

There are two issues to solve:

1. I can't drag an item above the readonly folder if that folder is the first in the list.
2. I can't drag the readonly folder itself to a different spot in the tree.

Both of these should be possible:

cant.drag.mp4

[mattnibs]

Tested on v0.27. I verified the first part- I can drag any item above a readonly folder. The second part doesn't work- I can't drag a readonly folder at all in a tree.