BUG: 0003204. Crosshair selection overridden by cross hair toggle.

This addresses a bug involving toggling and switching crosshairs:

1. If crosshair display is in mode "A"
2. Crosshair it toggled off in the GUI
3. Crosshair is set to mode "B" in the GUI

then the cross would display as "A" and not as "B".

The issue is in the order in which the "selection" signals are raised
relative to the "toggle" signals. When switching from off to any mode
the selection signals are raised first and then the toggled signals.

This ordering was aligned with the order in which the crosshair
node was modified relative to how the mode was cached (to set up for
toggling).

Caching the mode before setting mode addressed the issue.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22255 3bd1e089-480b-0410-8dfb-8563597acbee