Implement reporterOutput option

For making the tests pass, and not only for this reason, the `force` option now has one more behaviour. (now works much as any other grunt task out there)

`options.force` is false by default, (it stills works as before as I removed the `!`)

If `force` is true
- gsjlint will report errors but not fail the task. (new behaviour) allows passing through when writing the output to a file instead of failing the task in the console.
- gjslint will not fail the task when python is not installed on the computer. (same as before)

Added test for reporterOutput: run `grunt test`