Added Firelike Drawtype

Adds a new drawtype: 'firelike'.

Displays the provided texture at a 15 degree angle on the faces touching adjacent nodes if in the air, or on all sides when on the ground.

When the only node it touches is above it, it draws a the texture on the bottom of the node, not angled. (Should the direction of the texture be random?)

Demonstration (modified fire mod):
![In-Game Image](https://cdn.mediacru.sh/9cW-oCNvdghC.png)

Drawing code *heavily* modified from plantlike. :3
Oh, and textures are still animated.

**NOTES:**
Fire sometimes is left in mid-air with no nodes surrounding it after it burns a node. By default such fire will ~~not~~ be drawn.

Oh, I forgot to mention, when testing this branch, you won't see a difference unless you change minetest_game/mods/fire/init.lua - line 5 to this:

```
	drawtype = "firelike",
	pointable = false,
```