Remove scattering_objects folder for importing DiffractionObjects

[bobleesj]

Closes #182

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.31%. Comparing base (49bb353) to head (16937e7).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #189   +/-   ##
=======================================
  Coverage   97.31%   97.31%           
=======================================
  Files           8        8           
  Lines         261      261           
=======================================
  Hits          254      254           
  Misses          7        7           

Files with missing lines	Coverage Δ
tests/diffpy/utils/test_diffraction_objects.py	84.61% <100.00%> (ø)

[bobleesj]

@sbillinge ready for review

from

from diffpy.utils.scattering_objects.diffraction_objects import DiffractionObject

to

from diffpy.utils.diffraction_objects import DiffractionObject, PdfObject

[sbillinge]

Nicely done, @bobleesj thanks!