Removed old, unused, duplicate class named pqColorTableModel

In addition:

- removed unused pqColorTableDelegate class
- added missing export for the remaining pqColorTableModel

Change-Id: I3b30dcc970c40177b642cf05e6b6cc0c6ec15cee
Merge topic 'remove_duplicate_pqColorTableModel' into next

db6d2a7c Removed old, unused, duplicate class named pqColorTableModel