Updating platform names

Updating platform os names to reflect latest changes by @imartinezortiz affecting the release process.

New platform names:
"multiplatform-jre-win32", "multiplatform-jre-win64", "multiplatform-jre-macosx", "multiplatform-jre-linux-i386", "multiplatform-jre-linux-amd64"

These platform names are necessary for portable releases that embed platform-specific jres.

As the number of platforms has increased quite a lot, I've reated a separate class OS for these.