A more elaborate example with changing cursors

[jachin]

The main goal of this PR is provide a more elaborate example where the cursor changes as the Elm logo is dragged and dropped.

[jachin]

This is not done yet... there are problems...

Firefox

Firefox.-.Broken.Cursors.mov

✅ The hover cursor switches to grab
✅ When I start dragging the cursor switches to grabbing
❌ When I drag over a drop zone the cursor switches to move - instead it just stays as grabbing

Chrome

Chrome.-.Broken.Cursors.mov

✅ The hover cursor switches to grab
❌ When I start dragging the cursor switches to grabbing - instead it switches back to the default cursor
❌ When I drag over a drop zone the cursor switches to move - it seems to work the first time, but on subsequent drags it switches to a cursor with a green moving box. Maybe this is OK, but it's strange it's not always working.

Safari

Safari.-.Broken.Cursors.mov

✅ The hover cursor switches to grab
❌ When I start dragging the cursor switches to grabbing - instead it switches back to the default cursor
✅ When I drag over a drop zone the cursor switches to move