Add support for containsKey in JSONObject

JSONObject don't support containsKey.

    java.lang.UnsatisfiedLinkError: com.google.gwt.json.client.JSONObject.containsKey(Ljava/lang/String;)Z
        at com.google.gwt.json.client.JSONObject.containsKey(Native Method)
        at se.surikat.dashboard.client.JSONHelper.getJSONValueFromJSONObject(JSONHelper.java:65)
        at se.surikat.dashboard.client.JSONHelper.getJSONObjectFromJSONObject(JSONHelper.java:83)
        at se.surikat.dashboard.client.JSONHelper.getDimensionField(JSONHelper.java:13)
        at se.surikat.dashboard.client.JSONHelperTest.testGetDimensionNotAString(JSONHelperTest.java:124)


Have made a fix in JSONObjectParser 

    @PatchMethod
    static boolean containsKey(JSONObject jsonObject, String key) {
    Map<String, JSONValue> map = getInnerMap(jsonObject);
      return map.containsKey(key);
    }

which solves the problem