Summary:
Change the license of the source code from BSD + PATENTS to MIT.

Change `checkCopyright` to reflect the new license and learn some new file
types.

Generated with:

```
git grep BSD | xargs -n 1 ./scripts/checkCopyright -i
```

Reviewed By: jeremydubreil, mbouaziz, jberdine

Differential Revision: D8071249

fbshipit-source-id: 97ca23a