Dropzone is initialized

All tests expected to pass
Rename dropZoneOptions -> dropzoneOptions and slickGridOptions -> slickgridOptions
Better way to test callbacks
Separate slickgrid and dropzone callbacks into private objects
Basic dragdrop uploads
Tree and Leaf constructor takes an object of data

Allows extra metadata to be attached to th Tree
Allow id to be specified explicitly
Fix slow addItems
Add getItem and collapse methods of Tree and Leaf
Add expand() method of Tree and Leaf
Add method to ensure all nodes of a tree point to the same dataview
Update tests
Faster filter
Fix collapsing/expanding implementation

This fix ensures that the efficiency of the collapse filter is only
dependent on the size of the data but not the maximum depth of the tree