line graph redraw

I added a redraw method to linegraph, and fixed the physics page to use it and to actually change the data (which is probably all that you were missing before).

from the modified handleChangedValue:
``` javascript
// update the linegraph w/ the new data
dots.data[0] = electrons;
		
// redraw the dots
dots.redraw();
```

This pull also contains work in progress for the image widget, but I haven't done any additional work on this since we talked on friday.

Yes the redraw method duplicates much of what the draw method is doing. The next step will be to figure out how to have both methods utilize a common function or functions.

**edit**: ok, I just did that, I've refactored out a drawData_ method which is called by both draw and redraw. redraw currently doesn't do anything else, but it may at some point, which is why I'm not just calling redraw from draw.