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/EllipsoidRegion.java

@@ -136,6 +136,11 @@ public class EllipsoidRegion extends AbstractRegion {
     public void contract(Vector change) {
     }
 
+    @Override
+    public void shift(Vector change) throws RegionOperationException {
+        center = center.add(change);
+    }
+
     /**
      * Get the center.
      *