Remove superseded SelectionMover class

The SelectionMover class has been superseded by more flexible combinations of filters, scanners and utils. The replacements bring less dependence on the cursor node for positioning, allowing greater flexibility and re-use.

Removing this code and associated tests performs the final step necessary to close #224. In addition, this eliminates redundant line detection logic, so #225 is also closed by this as well.
While touching this code please improve the API dox to mention that this is about the last paragraph touched by the range, not the last paragraph of the document (wrong understanding took me some time, thankfully @adityab pointed me the right way in the end).