core: --user -- add basic.target an sort against it like --system does

units/user: default.target must be isolatable ... Activating default unit: default.target Default target could not be isolated, starting instead: Operation refused, unit may not be isolated.

units: introduce new Documentation= field and make use of it everywhere This should help making the boot process a bit easier to explore and understand for the administrator. The simple idea is that "systemctl status" now shows a link to documentation alongside the other status and decriptionary information of a service. This patch adds the necessary fields to all our shipped units if we have proper documentation for them.

relicense to LGPLv2.1 (with exceptions) We finally got the OK from all contributors with non-trivial commits to relicense systemd from GPL2+ to LGPL2.1+. Some udev bits continue to be GPL2+ for now, but we are looking into relicensing them too, to allow free copy/paste of all code within systemd. The bits that used to be MIT continue to be MIT. The big benefit of the relicensing is that closed source code may now link against libsystemd-login.so and friends.

drop support for MANAGER_SESSION, introduce MANAGER_USER instead