added asString method to WaterdropFormEnum and WaterdropTechniqueEnum;
added Waterdrop.java; WaterdropManager.java;
updated WaterdropPhoto.java to use new Waterdrop class;
updated ShowPhotoPageHandler.java and UploadPhotoFormHandler to use new WaterdropManager class;
added asserts for design by contract to WaterdropManager.java and WaterdropPhoto.java;
added test case for WaterdropManager;
added additional test cases for WaterdropManager;