Fix runtime error on Mac platform when setting the Title.  Was throwing NoImplemented exception because Title is checking if Window is null or not.  If it is still null at this point it will throw that error.  Moving it to OnLoad works.
Merge branch 'develop' of https://github.com/mono/MonoGame into xamarin
Merge pull request #2448 from mono/xamarin

Fix runtime error on Mac platform when setting the Title.  Was throwing ...