Improve RC residuals panel

[IvanHeriver]

The RC residuals panel could be improved with the following:

• add toggle button to display residuals in % (using Q sim as ref.) or absolutly (in m3/s)
• add the option to display standardized residuals (Y_stdres which is the residuals divided by sigma where sigma is sqrt(uobs^2+(g1+g2*Qsim)^2) i.e. structural uncertainty + observed discharge uncertainty)
• (maybe) add residuals uncertainty (deriving it using Y_stdres) but only feasible for absolute residuals