Clarify points vs. positions vs. steps concepts in SelectionMover

Significant work is still required in OdtDocument and other layers to
continue this cleanup work. No functional changes are intended by this
tidy-up.
Remove unnecessary local member id parameter

All consumers of this event check the memberid associated with the cursor
regardless. This filter therefore does nothing.
Cleanup OdfDocumentTests to push setup into createOdtDocument

This makes some more scenarios with range-selection more easily testable.
Because this is an OdtDocument level test, the cursor has also been upgraded
to an OdtCursor so it can be properly interacted with on the document.
OdtDocument.fixCursorPositions will preserve the current range selection

Previously, fixCursorPositions would always result in the cursor's range
being collapsed. This has now been extended to maintain the selection
whilst fixing the position of both the cursor and anchor nodes.