add missing method Polygon.addPoint(Point)

[bertsky]

This fixes compilation of GoogleJsonPageReader.handleBoundingBox().

[mikegerber]

It seems I've encountered the same build problem as @bertsky:

/home/mike/devel/prima-core-libs/java/PrimaDla/src/org/primaresearch/dla/page/io/json/GoogleJsonPageReader.java:320: error: method addPoint in class Polygon cannot be applied to given types;
                                                        ret.addPoint(getPoint(vertices.get(0)));
                                                           ^
  required: int,int
  found: Point
  reason: actual and formal argument lists differ in length
/home/mike/devel/prima-core-libs/java/PrimaDla/src/org/primaresearch/dla/page/io/json/GoogleJsonPageReader.java:321: error: method addPoint in class Polygon cannot be applied to given types;
                                                        ret.addPoint(getPoint(vertices.get(1)));
                                                           ^
  required: int,int
  found: Point
  reason: actual and formal argument lists differ in length
/home/mike/devel/prima-core-libs/java/PrimaDla/src/org/primaresearch/dla/page/io/json/GoogleJsonPageReader.java:322: error: method addPoint in class Polygon cannot be applied to given types;
                                                        ret.addPoint(getPoint(vertices.get(2)));
                                                           ^
  required: int,int
  found: Point
  reason: actual and formal argument lists differ in length
/home/mike/devel/prima-core-libs/java/PrimaDla/src/org/primaresearch/dla/page/io/json/GoogleJsonPageReader.java:323: error: method addPoint in class Polygon cannot be applied to given types;
                                                        ret.addPoint(getPoint(vertices.get(3)));
                                                           ^
  required: int,int
  found: Point
  reason: actual and formal argument lists differ in length
4 errors

[mikegerber]

This PR fixes the problem and the project builds!