make column headings more consistent in data files

[iantaylor-NOAA]

Initially posting as a draft pull request to foster discussion before marking ready for review.

Concisely describe what has been changed/addressed in the pull request.

• Aligns a few inconsistencies in the column headers written to data_echo.ss_new (and expected and boostrap data files).
  • more consistent use of lowercase headers
  • "season" to "seas" (which is more common)
  • "partition" to "part" (which is more common)
  • "SampleSize" to "Nsamp" (which is more common)
  • make things match better across the three types of data ss_new files as well as echoinput (in part because this helped confirm that the changes above were made throughout)
• Change "yr" to "year" as suggested in this comment and the one below from @kellijohnson-NOAA https://github.com/r4ss/r4ss/issues/512#issuecomment-1438728972.
• Changes are in parallel with changes in the r4ss function to read the data files initiated thanks to @e-perl-NOAA in https://github.com/r4ss/r4ss/pull/945.

What tests have been done?

None so far. The changes should only be to comments, not numerical values, so I don't think additional testing of SS3 itself is needed.

What tests/review still need to be done?

The read/write of data files by r4ss should be tested against these changes along with the status-quo output.

Is there an input change for users to Stock Synthesis?

[x] No, there was no input change.

[iantaylor-NOAA]

@e-perl-NOAA and I discussed the changes to SS3 and r4ss just now and made a few more tweaks, but we think this is now ready for review from @Rick-Methot-NOAA. We will also merge the parallel issue cleaning up r4ss column headers: https://github.com/r4ss/r4ss/pull/945.