Build synfig_icon.ico as well as sif_icon.ico

Install Win32 icons into the pixmaps directory too
Fix 1655158: Use the .ico files instead of synfigstudio.exe
Fix 1655155: Remove unused images from the Win32 installer package
Fix 1655149: Generate the correct BMP format with imagemagick 6
Patches by Dmitriy Pomerantsev (Atrus)

git-svn-id: http://svn.voria.com/code@237 1f10aa63-cdf2-0310-b900-c93c546f37ac