af-main: Handle users from the system scope

To simplify the management of users while keeping
systemd as launcher, this evolution anchors the
framework in the system level.

This also introduce a new version of afm-system-daemon
that is 100% a binding of the binder and that
consequently offers natively a websocket API.

Change-Id: I1bbb48d0c01d0f6fd3c8dfca90febbe8147cf204
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/12139
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Stéphane Desneux <stephane.desneux@iot.bzh>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>