FYI: Work on replacing sounds from non-free sources

[Wuzzy2]

This issue is just for your information. Today I have started working on making replacements for the sounds that were derived from non-free source files. I have looked all over Freesound.org and edited a lot, and I am mostly happy with the result now.
I have no idea how to test the sounds in-game, however. A hint would be appreciated.
I didn't touch sounds that came from non-free sources for now, for the off-chance that any of the original sound editors appear again and give their OK to switch away from Sampling Plus. (see #6)

I hope to soon (TM) post a PR so you can review the new sounds.

[Wuzzy2]

See #8.