Add model fit display

[davidborland]

"Would it be possible to have a way of assessing how good the model fit is to experimental data? This would allow users to generate a parameter set specific to their experimental system and quantitatively compare this set to other experimental systems, e.g. cancer cell lines where proteins may be lost or overexpressed."

[davidborland]

Added model fit display, with drop downs to select simulation track and data track for comparison.