HMI implements Last User Context

We need a mechanism in the HMI to implement Last User Context (LUC). The implementation could be as simple as creating a link to app's desktop file (see GDP-555) on a specific path each time an app get's focused and removing it when it looses focus. Then on startup, HMI launches the app if it sees the link on the specific path. Or we could involved persistence subsystem. In any case, we'll need writable filesystem to implement this.