Cleaned up code in R2eff estimate module, by making each function independent of class.
This is to give a better overview, how the different functions connect together.
task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.
Authored by: tlinnet 2014-08-28
Parent: [r25403]
Child: [r25405]
