Add QtSingleApplication Source Files

The source files from the qt-solutions repository,
git://gitorious.org/qt-solutions/qt-solutions.git, for
QtSingleApplication have been added to apps/opencs/qtaddons. Also, the
changes to apps/opencs/main.cpp have been made to utilize the
QtSingleApplication library.

** Does Not Build **
There is a linker error when building with this change. OpenCS will not
be built.
Remove Unnecessary Qt Addon Source Files

The PRI files are not needed since OpenMW uses CMake.
QtSingleCoreApplication is only used for non-GUI applications.
Qt Add-on Changes to OpenCS CMakeLists.txt

The OpenCS CMakeLists.txt file is updated with the Qt add-on header and
source files.

** This commit is unable to build OpenCS. There are errors with
QtLockedFile.