Draft: Gather 1d interpolators
This is a draft to unify the "basic" interpolators.
- added new header-file
1DInterpolators.h
(name debatable), containing all 1D-interpolators - remove and replace 1D-interpolators from
AlphaS_Ipol.cc
+ the 4 PDF-Interpolators - remove unused interpolators from
AlphaS.h