Move loading of the config from ConfigBase to Config

Resolves #236
Move stream operators in Config to top to fix their lookup
Move initializer list of a QStringList to stream operators

Fixes clang build
Add a test to check if config is initialized right on construction
Fixed autologin
Merge pull request #241 from AnAkIn1/fixautologin

Fixed autologin
Fix running SDDM under a Plasma 5.0 desktop.

When running SDDM under a full Plasma 5.0 desktop, the integration plugin tries
to access the arguments to figure out a configuration file name.  However, as
argc in SDDM::GreeterApp was passed as a temporary into a QGuiApplication, which
takes argc as a reference, the reference to argc is no longer valid and the
application segfaults.  Fix by having GreeterApp take argc as a reference.
Merge pull request #242 from MJDSys/KDEFIX

Fix running SDDM under a Plasma 5.0 desktop.
Similar to c4cfeb6bbf8d, avoid crashes due to bad references.

Make sure argc is always valid when QCoreApplication access it, by keeping
it as a reference to argc from main.
Merge pull request #243 from MJDSys/argc_fix

Similar to c4cfeb6bbf8d, avoid crashes due to bad references.
Append failsafe session

Failsafe is always the last session to be added to the model, this
makes it the default session only if there are no other sessions.

Closes #235
Exit loop as soon as last session is selected

No need to continue any further when the last index is set.
Move and update the INSTALL file.
Merge pull request #244 from jleclanche/master

Add a basic INSTALL file
Update man pages

Fixes #231
Update changelog
Add contributor

Add Matthew Dawson <matthew@mjdsystems.ca>
Bump version to 0.9.0
Move X11 specific code from Display to DisplayServer

A step forward for a display server agnostic sddm.
With Wayland support coming soon we want display server specific code
not scattered all over the place.
Set HAVE_SYSTEMD when building with systemd support