Additional settings unit tests

- Created own file for testing `columnsService`
- Testing the existence and `getColumns` function of `columnsService`
- Testing `defaultSettings` object of settings
- Testing of `spreadsheetSettingsController` and initial values
- Updated mock-data.js to have am empty column for testing the removal of it
- Adding mock files to the list of settings unit test dependencies
Merge pull request #64 from stulees/chore/settings-unit-tests

Additional settings unit tests