[Feat] Consolidate some CSV files with author lists

[echoix]

Thanks for your efforts.

We have a number of CSV files, perhaps some could be merged? Their origin is from CVS/SVN times with a different than GitHub write access model which is no longer in place:

• contributors.csv
• contributors_extra.csv
• translators.csv
• utils/git_author_github_name.csv
• utils/svn_name_git_author.csv
• utils/svn_name_github_name.csv

In case of structural changes (e.g., merging selectively) also a GUI change would be needed:

wxpython/gui_core/ghelp.py

            contribfile = os.path.join(os.getenv("GISBASE"), "contributors_extra.csv")
            contribfile = os.path.join(os.getenv("GISBASE"), "contributors.csv")
        translatorsfile = os.path.join(os.getenv("GISBASE"), "translators.csv")
                label=_("%s file missing") % "translators.csv",

However, maybe better done in a separate PR.

Originally posted by @neteler in #4563 (comment)