Overhaul the Visual Studio 2010 Projects

Give the Visual Studio 2010 Projects an overhaul, by using property sheets
to consolidate commonly-used items, so to ease future maintenance, and move
all the projects to MSVC_Net2010.

	* MSVC_Net2010/atkmm-build-defines.props:
	* MSVC_Net2010/atkmm-version-paths.props: Add property sheets to
	  consolidate the commonly-used items, so that projects can refer
	  to them.
	* MSVC_Net2010/gendef/gendef.vcxproj:
	* MSVC_Net2010/gendef/gendef.vcxproj.filters:
	* MSVC_Net2010/atkmm/atkmm.vcxproj:
	* MSVC_Net2010/atkmm/atkmm.vcxproj.filters: Clean up using the
	  property sheets, and move to MSVC_Net2010/.  Adjust the file
	  paths accordingly, and add a PlatformToolset tag so that it would
	  be easier to support Visual Studio 2012/2013.  Also produce
	  .pdb files for Release builds.
	* MSVC_Net2010/atkmm.sln:
	* MSVC_Net2010/filelist.am: Adjust file paths accordingly.