Update tools versioning and libsodium paths.

This updates the GSL templates to emit VS2010 and VS2012 project files with tools version set to 4.0. This will prevent a warning upon compile when the 12.0 tools are not installed. All tools versioing is removed from imported .props files as this is not required and the files are intended to span platform versions.

This also reverts a path change to the existing VS2010 libsodium outputs. I am anticipating that libsodium will soon merge the pull request that updates these paths and also adds support for VS2012 and VS2013. In the mean time a workaround is to pull libsodium from [my fork](https://github.com/evoskuil/libsodium). This would be required for the VS2012 and VS2013 builds in any case, since libsodium does not yet include those platforms.