Improve ubuntu-system-service or look at systemd services

* ubuntu-system-services has 2 categories of functions
Non systemd/Ubuntu specific:
- set the proxy -> going to NetworkManager, maybe?
- keyboard support -> systemd
- is reboot required -> ubuntu specific, trivial code, would be easy to rewrite in C (maybe getting in aptd)?
- package system locked -> same
Systemd compat:
 SetHostName, SetStaticHostName, SetPrettyHostName, SetLocale, SetVConsoleKeyboard, SetX11Keyboard
 properties: get keyboard layout for X, the hostname...

 * gsd
 session tracking, org.freedesktop.login1 (logind)
Suspend() Hibernate() PowerOff() (dropped from upower?)
* gcc
systemd-localed: org.freedesktop.locale1, SetLocale() SetX11Keyboard()

Work items:
get ubuntu-system-services to exit after an idle delay (disconnect from the bus, run the loop to make sure there are no pending messages, then exit): POSTPONED
once the system wide proxy settings are moved into network-manager this service can go entirely (and the is_reboot_required/is_package_system_locked can either be done in C or move to e.g. aptdaemon: POSTPONED
[vorlon] review systemd interfaces to see which ones would need to be adapted to work on Debian/Ubuntu (keyboard handling for example): DONE
[seb128] talk to foundation-team about systemd packaging/splitting the helpers: DONE