Improve EnginioModel documentation

Change-Id: Iedbbd5816ec24fa5bde773766de1ec19aab1f711
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Use _data to avoid some casts

Change-Id: Icb7a71343507154245093ab66541e5c75cd505f9
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>