Cleanup FvwmPager's window handling methods.

[somiaj]

Remove a lot of duplicate code around the creation of, the moving of,
hiding of, and even the destruction of the mini XWindows FvwmPager
uses to represent the real windows.

• Remove ReConfigureIcon(), the method MoveResizePagerView() in ReConfigureAll() was already updating the icon windows. No need for a specialized function.
• Remove all the logic from the pager view's approach of creating and destroying windows as they came in and out of view of the pager. Instead do the same thing as the icon view, just move all the windows out of view. Desk[0] is used to stash all windows that don't have a home otherwise. Now it can be assumed that the windows always exist and no longer a need to check for that.
• Take all the methods that would use CalcGeom() to update the windows, and combine all the code into single methods. CalcGeom() is now called in a single location, and the creation of, and managing of all windows is uniform.

This work so far so good in my tests, managing behavior of the windows has become exponentially easier.