Removes qtconnectivity_experimental.bb which is not needed anymore since asteroid-btsyncd is implemented over BlueZ's GATT DBus API

Setup permissions so that timed can change time: includes changing the connman's dbus allowing policy, adding a postinst script ran at boot to add CAP_SYS_TIME to timed-qt5 and add xattr to the DISTRO_FEATURES so that setcap is compiled

Set QT_DIR_NAME to an empty string so that Qt specific binaries are no longer installed in odd not-in-PATH places like /usr/bin/qt5/. It also removes the need for some ugly sed hacks. Cf: https://github.com/meta-qt5/meta-qt5/blob/master/classes/qmake5_paths.bbclass

Factorizes code from asteroid-image and asteroid-image-dev in the asteroid distro and the asteroid-image.bbclass