Layering saved line under/over green lines

[KatieWoe]

For phetsims/qa#277 and phetsims/qa#278
The green line appears to layer over the saved lines, but the pointer tool sticks to the saved lines over the green lines when they overlap. Not sure which is intended to be out front.

[pixelzoom]

This seems similar to #89, but involves a saved line and a "standard" line (y=x, y=-x).

[amanda-phet]

@pixelzoom thanks for finding that issue- I was looking for it! If we can prioritize the active/black line, then green line, then gray/saved line, I think that makes the most sense.

[pixelzoom]

The problem was that the model and view were using different orders for the lines. Fixed in the above commits. The order in model and view is now: interactive line, standard lines, saved lines.

@KatieWoe please test in master. Here's a quick test procedure that covers all of the cases:

1. Start Graphing Lines.
2. Go to Slope-Intercept screen.
3. Change interactive equation to y = 4/4 + 0
4. Press "Save line"
5. Check the "y=x" check box.
6. Put a point tool at (2,2). It's display should be black (interactive line)
7. Change interactive equation to y = 5/4 + 0. The point tool's display should change to green (y=x).
8. Uncheck the "y=x" check box. The point tool's display should change to gray (saved line).

[KatieWoe]

Looks good on master

[pixelzoom]

Pending regression testing in 1.3.0-rc.2.

[KatieWoe]

Looks good on both rcs.