Add missing textures and models from Chorus' Version

This also helps in preparing for the Nether Update (1.16). Textures were
optimised using OptiPNG by:

optipng -o7 -nx

followed by a second run with the defaults.

assets/minecraft/textures/item/potion_overlay.png.mcmeta

@@ -0,0 +1,7 @@
+{
+	"animation": {
+        "frametime": 3,
+		"interpolate": false,
+		"frames": [0, 1, 2, 3, 4, 5]
+	}
+}