Grammatical number support for item names [CR]

Okay, this PR adds proper grammatical number support for item names. This is a continuation of #7141.
It is theoretically finished and needs now to be tested.
If this gets cleaned up and merged, fixes #4649.
Fixed #5883 already.

Item types as well as JSON entries get an extra entry, called “name_plural”. This is for the English (!) plural form of the string, whereas “name” is only intended for the singular form now. This has been done already.
For English, there is now a default behaviour: If name_plural is missing, the game assumed the same text as name + the letter “s”. Example: “plastic bottle” → “plastic bottles”. This behaviour only applies to English and is really just for convenience reasons.

Affected areas (grammatical number is used there successfully):
* crafting menu
* ingame messages (eg. “You drop your X”)
* construction menu
* inventory UI

To all the items in JSON (not in mods) a plural form of the name has been added.

The general “writing style” (eg. as in the inventory UI) has been changed from “5 x knife” to “5 knives” (the “x” has been removed).

Also done has been:
* rewrite string extraction scripts for the translations. This is important, without that the translations WILL break. I could also use some help with that.
* add plurals for items from mods, maybe

TODO:
* ??? (tell me what I forgot)

Status: Testing phase. This PR theoretically done, but please do not merge yet. Testing from other people is requested, just to be sure.