Write relative paths instead of absolute paths in .pot- and .po-files.

Currently both .pot- and .po-files get absolute paths (`#: C:\Dev\src\ProjectName\Views\Layout.cshtml:123`) which differs between developers in our project. These proposed changes will persist a relative path, based on the location of the web.config file passed to the postbuild tool, resulting in `#: Views\Layout.cshtml:123`