Removed obsolete code

SessionController.countStepsToNode is superseded by
OdtDocument.getDistanceFromCursor. All these checks are now done within
other layers
Don't modify window selection during drag

Resynchronising the shadow cursor back to the window during a drag or
mouse-move operation is ignored in Chrome & FF, but causes exceptions
and strange selection behaviour in IE. There is no benefit to doing
this, as the selection is resynchronized on mouse-up regardless.
Don't synchronize the shadow cursor to window selection and back

The shadow cursor has a stand-alone range that can be passed straight
into the processing logic that updates the input member's cursor.
Improve robustness of virtual selection around collapsed whitespace

An individual range may have no client rectangles if it is not visible
on the screen. In text nodes, this often means a sequence of collapsed
whitespace, or discarded whitespace at the start or end of an element
with "display: block" properties (e.g., p or HTML div).
Merge pull request #159 from peitschie/virtual-selection-fixes

Virtual selection fixes