Refs #8624  improved time domain

both tmin and tmax have been extended to make sure we obtain a
sufficiently complete frequency spectrum after doing the
fourier transform

modified: StretchedExpFT.py
modified:   StretchedExpFTTest.py
Refs #8624 Impose limit on time domain size

Extension of the time domain may create a too large one, thus
lengthening the fitting in excess

modified:   StretchedExpFT.py
modified:   StretchedExpFTTest.py
Merge remote-tracking branch 'origin/feature/8624_improve_time_sampling_stExFT'