Added methods to calculate optimal map size given a geo boundary.

- From zoom level 20 to 1, once find a size that contains the whole boundary, then the size will be used to retrieve map image from google

#story[928]

src/main/java/seng302/models/map/MapGeo.java

@@ -1,5 +1,9 @@
 package seng302.models.map;
 
+/**
+ * A class represent Geo location (latitude, longitude).
+ * Created by Haoming on 15/5/2017
+ */
 class MapGeo {
 
 	private double lat, lng;