Add support for FOC validation. Closes #3. Closes #5

Also changed line endings on the .travis.yml to remove `^M` line endings.

- [x] Validates missing files
- [x] New shell for testing FOC-valid plugins
- [x] Only optionally runs `composer install` if the `composer.json` exists
- [x] Add a `setup.sh` which can perform all the necessary changes to a plugin to make it FOC compatible
- [x] Add documentation for setup.sh. 

Note this will need a bit of work once #10 is merged to make the validation script run correctly, but I don't foresee that being a big issue.