now properly removing callbacks in dispose()

Change-Id: I43063bffec8eaa0d28d67da8540576d80a901c38
now removing hash map entry when column is disposed

Change-Id: I439523c566962097a8f3aee5114688d618b3b3dc
now disabling generated sort function when column is disposed

Change-Id: I945d22eecc0562fc2da0a360fc57406de999f04f
Now triggering callbacks when internal column is disposed, and no longer
making unnecessary function calls.

Change-Id: Ifb81f22735853bc95b8feb69d7fc9c16ec7fb873
now cleaning up / disabling everything when column is disposed

Change-Id: I0a0feec69dd86ff7083a6e3d3433d9bc26040654