Added setters to applicable MaterialData classes.

By: sunkid <sunkid@iminurnetz.com>

paper-api/src/main/java/org/bukkit/material/Lever.java

@@ -37,6 +37,14 @@ public class Lever extends SimpleAttachableMaterialData implements Redstone {
         return (getData() & 0x8) == 0x8;
     }
 
+    /**
+     * Set this lever to be powered or not.
+     * @param isPowered whether the lever should be powered or not
+     */
+    public void setPowered(boolean isPowered) {
+        setData((byte) (isPowered ? (getData() | 0x8) : (getData() & ~0x8)));
+    }
+
     /**
      * Gets the face that this block is attached on
      *