good re-write of D&D with generic non jquery code. this fixes the following:
- #1329 D&D wasn't working correctly in 2.0.0-rc
went through entire code with fine comb. "had to change 'drop' signature to have 2 elements (original drag and helper) do handle both cases - #1102 we no longer make a copy when dragging between grids (just re-parent)
so all actions and settings stay the same.
Only time we make a copy is if dragging from an external toolbar and user has helper to clone item - #1335 some fixes for new
load()API