Fix some crashes in EnginioQmlModel

Change-Id: I172819f1c16b21c904a00edcc94e2a07d162dfe7
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Use correct forward declared header

Change-Id: I81cbe9c16c310824fc8da165e3302846a6e65762
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Leave us some space to grow in EnginioModel::Roles.

Change-Id: I7c002ee9b10f872592abdc7dd5f9e1a3b67f3749
Reviewed-by: Andras Becsi <andras.becsi@digia.com>