Simulation runs "continuously" (actually in automatically repeated short
bursts).

Initially, the simulate button is used to start the simulation running.
The label changes to "pause". Pausing halts simulation, and label
changes to "run", which restarts simulation, etc.
Text boxes below sliders now display value of source/sink that is
adjusted by the slider.  This is done by hand, since the signal/slot
method in QtDesigner doesn't allow for connecting to the setText method.

Also, adjusted the continuous simulation parameters so that it is closer
to real time.
Merge pull request #1 from codecurve/master

Update my fork to the latest?