Change some things in the way OpenGL selection is done

Change some things in the way OpenGL selection is done

It now happens on button press, instead of happening on button release.
The clicked atom is highlighted in a separate color (currently some
shade of purple, tell me what you think) even if it is not selected. The
point of that is that this clicked atom is going to play a very
important role in the mouse navigation system I plan to write. Any
rotation/move will be done with respect to it. So I thought that this
special role of this atom should correspond to a visual highlighting.

M    kalzium/src/kalziumglwidget.h
M    kalzium/src/kalziumglwidget.cpp

svn path=/trunk/KDE/kdeedu/kalzium/src/kalziumglwidget.h; revision=566143