Added OpenGL selection code.

Added OpenGL selection code.

Single left click on an atom now selects/deselects it, if the mouse
didn't move between button press and button release. Some tolerance (2
pixels) added to make that usable with imprecise pointing devices.

TODO: notify the treeview (currently it doesn't get updated).

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

svn path=/trunk/KDE/kdeedu/kalzium/src/kalziumglwidget.h; revision=566121