Exit loop as soon as last session is selected

No need to continue any further when the last index is set.
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
Log display server command line

For debugging purpose.
Turn DisplayServer into an abstract class

Move Xorg specific code to XorgDisplayServer, this will allow us to
support multiple display server.
Update change log
One CMakeLists.txt file for each subdirectory

It's easier to work with separate CMakeLists.txt files, one for each
subdirectory.
Remove Arch Linux packages

No point in having those here, Jerome is maintaining them
on AUR.
Remove Qt 4 support

The time has come, SDDM is finally a Qt 5 only software.

[ChangeLog][General] SDDM now requires Qt 5.
Flush log file

Writes to the log file immediately.

[ChangeLog][General] Flush any buffered data to the log file,
this writes immediately all the log messages.

Issue: #182
Remove trailing whitespace
INSTALL: Remove -DUSE_QT5 and list the remaining options

Closes #249
Replace QLatin1String with QStringLiteral
Add initial Kazakh translation.

[ChangeLog][Translations] Added Kazakh translation.
Don't override pam environment variables

When using pam_env users are allowed to provide environment variables
to SDDM.

This is often used to customize PATH like Debian does.
However we overwrite those environment variables with our own.

What happens on Debian is that we overwrite PATH with a less
complete version.

Make sure pam variables are not overridden.

Closes #256

[ChangeLog][Behavioral Change] Don't override pam environment
variables.