Uptake curve axis range

[werpuc]

For uptake curves, it would be useful to see the maximal threshold. For fractional values it is easy - it is 100%. For absolute values it is a little more complicated and the threshold should be equal to maximal possible uptake.

So, this should be included:

• in the package function, plot_uptake_curve
• in the GUI. the sliders should be updated dynamically when the chosen peptide is changed. this may be a little tricky.