Added functionality to plot R1rho R2 as function of effective field w_eff, for the R2eff model.
Also renamed a function, to better reflect is functionality.
The hard-coding of which models to plot, has been removed.
If the exp-type is R1rho, then the plotting will commence.
sr #3124(https://gna.org/support/?3124): Grace graphs production for R1rho analysis with R2_eff as function of Omega_eff.
sr #3138(https://gna.org/support/?3138): Interpolating theta through spin-lock offset [Omega], rather than spin-lock field strength [w1].
