Ranking Criteria updates

[pishifat]

mostly small changes

clarified some glossary words in osu rc: https://osu.ppy.sh/community/forums/topics/898895
added recommendation for unknown chinese metadata: https://osu.ppy.sh/community/forums/topics/904342
clarification for 1/4 and 1/2 rhythm spacing guideline: https://osu.ppy.sh/community/forums/topics/891732 (generalized this one based on review)
adjusting for mistake in letterboxing rule/guideline: https://osu.ppy.sh/community/forums/topics/918503
a few metadata clarifications: https://osu.ppy.sh/community/forums/topics/885418
and some formatting fixes for song setup settings
...and a couple mistakes fixed on the mania rc

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[Xinnoh]

I don't know how to suggest changes to parts of the file that you haven't changed
Mania RC fixes
use less keys, -> use fewer keys
amount of keys -> number of keys (amount and less is used for non countable things)
favor -> favour
9 consecutives -> 9 consecutive
in a trills -> in trills

[RushFTK]

how about add changes in #2293 if no problem?

[RushFTK]

- **No column can be left empty.** If you want to use fewer keys, change the amount of keys in the Song Setup.

[RushFTK]

- **No column can be left empty.** If you want to use fewer keys, change the amount of keys in the Song Setup.

i made mistake, really dont know how to use that, even delete it ,sry to make troubles.- -