relax SVN archive

EXP_TYPE_R2EFF = 'R2eff/R1rho'
EXP_TYPE_NOREX = 'No Rex'
EXP_TYPE_NOREX_R1RHO = 'No Rex: R1rho off res'

These are used to add meta-data information to each model, making it possible to make
a nesting function, determining which model to nest from.

sr #3135(https://gna.org/support/?3135): Optimisation of the R1 relaxation rate for the off-resonance R1rho relaxation dispersion models.