Add a method to remove a PolygonEntity from a PolygonGraph

* Refactored removeEntity() method for LandRGraph and LineStringGraph
* Added a removeEntity() method  for PolygonGraph
* Added related tests
 Add a method to clean Edges of a PolygonEntity
    
	* Added A cleanEdges() for PolygonGraph
    * Refactored removeEntity() method  for PolygonGraph
    * Added related tests
Add a method to get PolygonEntities by Min Area
    
        * Added a getPolygonEntitiesByMinArea() method for PolygonGraph
        * Added related tests
 Add a method to merge two PolygonEntities
    
  * Added a mergePolygonEntities() method for PolygonGraph
  * Added related tests