Remove all syncing between selection size and text boxes on main form

This is a crucial part of refactoring the current selection code - the
pdSelection object should not be directly updating interface elements AT
ALL
Clean-up selection node mouse detection code

Previously, horizontal or vertical resizing was allowed along each
entire "virtual" line of the image.  Now it is constrained to being
within image bounds (+/- the current mouse accuracy setting)
Change mouse down behavior when outside selection bounds

Basically, clear the current selection and start a new one from scratch
Rebuild main form selection text boxes as control array
Allow fine-grained en/disabling of main form selection controls

Required for transformable vs non-transformable selections -
non-transformable ones still allow the setting of stuff like AA, but
they do not allow coordinate requests.  So certain controls must be
en/disabled accordingly.
Update saved selection test files to newest selection file version
Massive selection code refactoring

Many smaller selection issues should be fixed with this commit.  This
does not fix ALL issues, but it is a huge step toward cleaning up PD's
selection code.

The most important change is that all interface code has been completely
removed from the pdSelection class.  This alone fixed a number of bugs,
as well as improving performance (by avoiding multiple pieces of code
redrawing the screen independently).

One rather serious known issue is that Undo/Redo and loading selections
from file do not update the matched interface elements (e.g. the
feathering radius scroller is not updated with new feathering radii
values by these actions).  This fix is forthcoming.