Visual Studio Builds: Link to LibPNG-1.6
Add note on libpng for Visual Studio Builds

Tell people that the Visual Studio project files will normally link to
the latest stable release series of libpng that is supported by the
codebase, and people can still use libpng 1.0.x-1.6.x if they choose
to do so by changing some settings during the build.
[l10n] Updated Italian translation.
Updated Norwegian bokmål translation