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
Let string extraction scripts also extract plural field

Now the .pot file generated by update_pot.sh will contain proper msgid_plural fields for item names.
It has been tested roughly to work with translation files.
Use nname() instead of name in item wish menu

nname() is the function to get an item type’s name with respect
of grammatical number. Warning: Using name only returns the
English name now!
Add plurals to “EW pack” and “Oldies Pack” mods
Fix small typo in ammo.json
Add some comments regarding grammatical number support
Speacial treatment of translation handling for fake items; and don't automatically add msgid_plural for non-items
Fixed text of dropped item types

If multiple items of 2 or 3 types laid on the floor, the game falsely mentioned the same item type twice or three times.
Example: You have 8 hammers and 8 scissors on the floor. The game displayed “You see here 8 hammers and 8 hammers”.
Pluralize boxing gloves
Fix dropped item display even more