delay very first start of sysimg_update by 10 min

to allow ntpd to settle and negotiate ...
add class for remind installed apps and 1st sample

* add a bbclass for recording important versions for our target image.
* add system-image for demonstration and prepare system-image-update based on it
Update sysimg_update

* Update to recent git-version to be future prove and better deal with chosen download images
* rely on newly introduced system-image for versioning ...