modify effects

- snake has a nice tail
- random is not so fast anymore
- merge sparks and sparks-color
- make more params available in json files


Former-commit-id: fc2a4f6f6ce2b44a35a75a9c0dbe36504b790be9

effects/sparks.json

@@ -3,5 +3,12 @@
 	"script" : "sparks.py",
 	"args" :
 	{
+		"rotation-time" : 3.0,
+		"sleep-time"    : 0.05,
+		"brightness"    : 1.0,
+		"saturation"    : 1.0,
+		"reverse"       : false,
+		"color"         : [255,255,255],
+		"random-color"  : false
 	}
 }