Facility items 003 chemicals (reprise) [WiP][CR]

Using the discussion from https://github.com/CleverRaven/Cataclysm-DDA/pull/9215 I've put up a tiered system for chemicals and populated it with the first batch of chemicals and a nice bomb to keep things interesting.

In total, I am planning some 30 chemicals (15 out of the way already, 10 more shortly) and some 20 devices (among them: Thermite, RDX, HMTD, TCAP, Powder charge, Hexamine, Smoke curtain, Rocket Candy, Home-made rocket).

Please comment on what do You think of these ideas and tell me if there is something obvious, that I should add to the list.
This is invalid json.

Have you even tried to launch a new game? Starting the cataclysm program is not enough, you need to load a new game to make the program load (and check) the json.

The json  format does not support comments, but you can add valid json entries that are effectively ignored like this:
```
"//": "your text"
```
Some of the files there already contain comments of that form.