terminal: drop unfinished code This drops the libsystemd-terminal and systemd-consoled code for various reasons: * It's been sitting there unfinished for over a year now and won't get finished any time soon. * Since its initial creation, several parts need significant rework: The input handling should be replaced with the now commonly used libinput, the drm accessors should coordinate the handling of mode-object hotplugging (including split connectors) with other DRM users, and the internal library users should be converted to sd-device and friends. * There is still significant kernel work required before sd-console is really useful. This includes, but is not limited to, simpledrm and drmlog. * The authority daemon is needed before all this code can be used for real. And this will definitely take a lot more time to get done as no-one else is currently working on this, but me. * kdbus maintenance has taken up way more time than I thought and it has much higher priority. I don't see me spending much time on the terminal code in the near future. If anyone intends to hack on this, please feel free to contact me. I'll gladly help you out with any issues. Once kdbus and authorityd are finished (whenever that will be..) I'll definitely pick this up again. But until then, lets reduce compile times and maintenance efforts on this code and drop it for now.

bus-proxy: turn into multi-threaded daemon Instead of using Accept=true and running one proxy for each connection, we now run one proxy-daemon with a thread per connection. This will enable us to share resources like policies in the future.

consoled: add a unit file The unit file is statically enabled, but still requires --enable-terminal to actually get installed.

remove bus-driverd, the interface is now handled natively by bus-proxyd

bus-driverd: support user mode

bus-proxyd: support --user bus address

units: rename halt/hibernate/kexec/poweroff/reboot/suspend to systed-xxx These service units also execute our own code, hence rename the accordingly and prefix them with systemd-

drop support for MANAGER_SESSION, introduce MANAGER_USER instead