Revert "Do not generate an cookie as root when loading"

This reverts commit fed4519b3fa90f92cef1a4f9802eabc9692508c1.
Don't chop last character when logging to journald

Messages never ends with a new line character so there's no point
in chopping the last character.

This fixes log messages missing the last character and closes #185.
Change authDir into stateDir
Set the auth file name to be the display name only
Change the user and group of the auth file to the sddm user when possible
Don't create .Xauthority for the sddm user
Merge pull request #180 from AnAkIn1/authfilefix

Fix cookie generation and set the correct cookie path for the greeter
Use standard installation paths

CMake already has support for standard installation paths
including GNUInstallDirs.  Remove our definitions and use theirs.

While we are here, use a more conventional path for data files.
Merge pull request #189 from plfiorini/cmakeinstalldirs

Use standard installation paths