Add a demo mode in to the B2Qt demo launcher (required for QTBUG-72563).

Demo mode will turn on automatically after set time, and rotate through B2Qt Demo launcher apps main UI's (but not necessarily all possible UI's) in a pre-determined script

Demo mode will turn off and application will return to B2Qt launcher UI upon user interacting with the device.

The demo mode is configured ON (after power on) by default.

There needs to be a setting to turn demo mode ON and OFF, and to set time in minutes after which the Demo mode will kick in and start scrolling the UI.

The Demo mode should be implemented in a way, that when we remove or add more apps in to the B2Qt launcher it is easy to adapt the Demo mode to this.