Fixed license for all basic types

Just a simple fix and nobody will bother to do it next time.
I did contact the last Mono.Xna team members and they had no problems with us using portions of their code within MonoGame.  They didn't give me explicit permission to relicense things...  so we can't just omit the MIT stuff.  This is mainly why we  haven't done this sort of bulk replacement of license info.

Ideally we can include the information in the LICENSE.txt like:

```
Portions Copyright © The Mono.Xna Team
(MIT license here)
```
Mono itself calls out difference licenses to different parts of their code base in a single LICENSE.txt file, so it seems like a reasonable thing to try to do.

I just don't know the right way to proceed with that.