use attendedsysupgrade-common package and rpc-sys instead of
rpcd-mod-attendedsysupgrade
luci-app-attendedsysupgrade: editable server url
the server url can now be changed. The solution is kept as simple as
possible to not introduce any lua code.
Small cleanup, but needs a refactoring.
Add acl rights to edit the attendedsysupgrade file
Add cgi-io as a dependencie to upload image to router
Signed-off-by: Paul Spooren <paul@spooren.de>