Use vt 1 when systemd support is available

systemd graphical mode uses vt 1 for display managers.
Add missing USE_PAM definition to Authenticator.cpp
Always go via PAM for autologin

This passes our session through the systemd PAM module that sets up
logind correctly, fixing a bug where polkit actions would not work
correctly in an SDDM session
Provide seat name and virtual terminal number to PAM environment variables
remove pointless pam checks in autologin
Merge pull request #168 from w41l/master

Add missing USE_PAM to Authenticator.cpp
Merge pull request #142 from davidedmundson/fix_autologin

Fix Polkit sessions with autologin
Merge pull request #167 from plfiorini/systemd

Use vt 1 when systemd support is available