Add throwable fire extinguisher

This PR adds throw-able fire extinguisher and flag "ACT_IN_FIRE". This flag activates the item if it placed in fire.

Potentially, this flag should be added to stuff like grenades and c4 for illustrating the idea that storage of flammable things in fire is really silly. Current issues are:
- The flag doesn't work properly with anything except throw-able fire extinguisher without updating the code;
- Item doesn't activate if fire appears after the item placement;
- Better description for throw-able fire extinguisher is welcomed.

Anyway, the PR is working as-is, and other features can be implemented later in separate PRs.

P.S. Inspired by http://youtu.be/WeWs8Aqo2Fk?t=18s