Move X cookie generation out of Session code.
Do not generate an cookie as root when loading

It's not used by anything
Remove explicit delete call to parented object

d->socket has the GreeterProxy object as a parent so will be deleted
anyway
Proxy messages from the greeter in SDDM output
Catch errors launching the greeter before we block.
Move generateName to a separate file
SocketServer generates it's own name

SocketServer is in charge of creating the socket name. It then exposes
the full socket path.

SocketServer is changed to not have m_started and the server in separate
states.
Only set session environment user/path if set
Start the greeter under the user sddm
Merge pull request #159 from davidedmundson/nonrootgreeter

Don't run the greeter as root
Add support for display setup script
Add missing DISPLAY and XAUTHORITY env variables