Debounce calls to ProjectManager._renderTree.

This is a possible fix for #9851. In my tests, this can cause a
dramatic speed up when lots of filesystem changes cause the tree
to be continuously rerendered.

I chose 100ms as the debounce time because that seemed quick enough that
users will not be waiting for their actions to be reflected in the tree.
Fix WorkingSetView test based on review feedback.
Use Jasmine's `waits` function instead of my own.

Also fixes JSHint error.
restore whitespace
Merge pull request #10120 from adobe/dangoor/9851-debounce-render

Debounce calls to ProjectManager._renderTree.