Add versions for components and improve sysimg_update

Add versions for components and improve sysimg_update

* Introduce version recording for components (added first core-component: system-image)
  + let hp-blob / xbmc being modified by Patrick (Tobias) and Per
* Update sysimg_update for better behavior on controlled restarts from RESTful API and improved check for what "recent" means (see https://github.com/rehsack/System-Image-Update/commit/7768ba6251bb979b3a9423cbac16318133452532)