Official Polymer compatibility

- Based on my PolymerRocks compatibility patch, featuring many improvements over it
- Less hardcoded object instances, allowing for easier addition of new variations

src/main/java/eu/midnightdust/motschen/rocks/blockstates/SeashellVariation.java

@@ -20,4 +20,10 @@ public enum SeashellVariation implements StringIdentifiable {
     public String asString() {
         return this.name;
     }
+
+    private static final SeashellVariation[] vals = values();
+
+    public SeashellVariation next() {
+        return vals[(this.ordinal() + 1) % vals.length];
+    }
 }