MSBuild fix property multiple value & quotation

1.Added support for multiple values as some MSBuild properties require this
2.Addded quatation to property key / values to support values with spaces
3.Adjusted tests to pass with new sematics
This enables properties like ReferencePath to be used whith cake.
Example fluent:

    MSBuild(solution, settings =>
        settings.SetPlatformTarget(PlatformTarget.MSIL)
            .UseToolVersion(MSBuildToolVersion.NET45)
            .WithProperty("ReferencePath", @"c:\temp\assemblies1")
            .WithProperty("ReferencePath", @"c:\temp\assemblies2")
            .WithTarget("Build")
            .SetConfiguration(configuration));

Example all att once:

    MSBuild(solution, settings =>
        settings.SetPlatformTarget(PlatformTarget.MSIL)
            .UseToolVersion(MSBuildToolVersion.NET45)
            .WithProperty("ReferencePath", @"\temp\assemblies1", @"\temp\assemblies2")
            .WithTarget("Build")
            .SetConfiguration(configuration));