Merge pull request #451 from jverkoey/indexPathForObject

Implement indexPathForObject: on NITableViewModel and NICollectionViewModel.
• Added table view cell types: NICaptionCell and NILongTextCell
• Added NILongTextInputFormElement for long text entry
• Fixed some code in NILongTextCell
• NILongTextInputFormElementCell now propagate text changes back to NILongTextInputFormElement
• NILongTextCell layout improvements
• Colour adjustment to NICaptionCell's details label