Updated the user documentation (as a result of #201).
Some minor cleaning up.
Addressed a small issue with Windows not handling threads very efficiently.

The issue was that a remaining call to
SingleCellViewWidget::simulationRunning() would be made after the
simulation has finished, thus making the plot non-interactive. So, now,
we set the interactive mode based on the actual state of the simulation.
Some minor cleaning up of our graph plotting widget code.
Some minor cleaning up.
Slight improvement to our plotting widget.
Slight improvements to our plotting widget.
Minor fix for our plotting widget.
Minor fix for our plotting widget.
Improvements to our plotting widget.
Slight improvement to our plotting widget.
Some minor cleaning up.
Now zoom in/out around the mouse position (closes #201). Also various improvements and quite a bit of cleaning up of our plotting widget.