MGFX Fix + Tests

This PR first fixes MGFX to support:
```
ColorWriteEnable = true;
ColorWriteEnable = false;
ColorWriteEnable = 0;
ColorWriteEnable = 1;
```
... in addition to `All`, `None`, `Red`, `Green`, `Blue`, and `Alpha` as valid values again.

This PR also includes a rough first pass at unit test support to MGFX content processing.  A lot more to do there still, but this is at least a start and will help begin to keep us from regressing in the future.