Bug 1017314: Load tutorial config in a loadConfig method.

* New unit tests, fixes existing FTU tests with setup.js and misc path/dependency issues
* Start tutorial preload in ftu UIManager.init
* Use l10nKey as property name in config
* Refactor Tutorial to loadConfig/ensureConfig and update tests accordingly
* Use shared mock_navigator_moz_setttings, delete the ftu one as its no longer used (c.f. bug 1017893)
* Remove unused data-maxstep attributes.