Fix keyboard layout settings reading and writting

Reading from setxkbmap's output to get user layouts and calling setxkbmap to set
new layouts are broken
Make the code compile with both Qt4 and Qt5.
Write Qt settings to lxqt.conf instead of the deprecated Trolltech.conf in Qt5.
Show cursors by using raw xcb calls since Qt5 does not support creating QCursor based on native cursor handle.