Rudimentary grammatical number support for items

First try in inventory UI
Add some test plural item names

Ammo in this case
Make crafting components respect grammatical number
Load name_plural field from JSON

If name_field is missing, append a “s” by default.
Fix item factory plurals and ammo examples
Create plural forms for other JSON items (without mods)
Small JSON fixes
Make construction menu respect grammatical number
Make inventory screen respect grammatical number
Make game messages respect grammatical number of items

The messages: “You see here X” and “You drop your X”.
Small JSON fix