Add bliss-cor-8 estimation

About

This update includes:

• [] The handling of the Nexus estimated_cor_frm_motor in fourier-angles and sliding-window COR estimators.
• [] A new octave-accurate COR estimator, which implements the older Octave/accurate algo.
• [] The fourier-angles COR estimator, which is the origin of this MR has not changed, except for the API, which is now aligned with other estimators.
• [] The near_pos option can take on values which are either a relative COR position, ignore, from_file. In case of none of the previous values, set to `ignore'.
  • ignore: disregard the value in Nexus file and acts as before.
  • from_file: tries to pick the value in Nexus file. Switch to ignore if fails.
  • Number: the user-provided COR value overrides the value in the Nexus file.

Tests were added to check this behavior. Add CoR estimation algorithm submitted by V. Valls (BCU), based on FT of angular pixel signals.