Improve 2D function support

[leek2]

Curvallis has rudimentary 2D function support. (ie Pt(V,T) so, 2 inputs, 1 output. This is really a 3D field. ) This is displayed in Curvallis as a series of lines. This works OK for EOS because each line is a constant temperature, and the X axis is density. Because pressure and energy increase with temperature, the lines stack nicely. However, there are some problems with this support:

1. Verify that if you change a value it is correctly written back to the file.
2. Display the temperature of each line. Since each line represents a constant temperature, we should have a display (different window?) that lists each temperature. High to low.
3. Even better would be some way to highlight a temperature line so you can see which you're working on.
4. Display a small set of lines (eg 3) and allow the user to "scroll" through the lines. So, if there are 100 lines in the table, display the bottom 3. Then when the user scrolls up once, lines 2-4 are displayed. Then 3-5, etc.