Displays update notification for user, but does not provide
automatic updates. Version comparison is based on string match,
so build dates are not relevant.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

Tested-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Michael Fritscher <fff@mifritscher.de>