Added Region.shift

- Provided a default implementation using expand+contract in AbstractRegion
- Overrid the implementation in the subtypes

src/main/java/com/sk89q/worldedit/regions/Region.java

@@ -88,6 +88,14 @@ public interface Region extends Iterable<BlockVector> {
      */
     public void contract(Vector change) throws RegionOperationException;
 
+    /**
+     * Shift the region.
+     *
+     * @param change
+     * @throws RegionOperationException
+     */
+    public void shift(Vector multiply) throws RegionOperationException;
+
     /**
      * Returns true based on whether the region contains the point,
      *