Update VS projects and fix test warnings.

I've created a branch in my own repo for the 1.0.0.0 release and NuGet packaging. These changes are intended for master and therefore match the current version.

The reverted changes to common props are not consequential, as these symbols were already defined in `libsodium.props`. The common props are not intended to be customized. If it is necessary to also apply customization to the Test project then `test.props` should be updated accordingly.