Improved DataModel context consistency and thread integrity

- Improved DataModel context consistency and thread integrity
- Enhanced ManagedObject context consistency and thread integrity
- Correctly obtain permanent object ID's when saving object to dictionary
- Use correct context when performBlock calls
- Added automatic cancelWatch in Watch dealloc calls (testing)
- Added contentHeight to DNTextView
- Added initial code to track current visible cell when list is updated
- Updated podspec version

Signed-off-by: Darren Ehlers <me@darrenehlers.com>