Refactored domain classes

Made the following changes:
1. Added blood group to the Patient class. I know it's not present in the existing application but I've seen a few medical patient entry form and exists in almost everyone of them and since we are targeting for a complete health record in long run I guess this field is a must for that.
2. Simplified Address class. We don't need to break it down to SUCH atomic level besides not every area has road numbers.
3. Added a date field in Diagnosis class. Since we've detached diagnosis form from the main patient info entry I guess we need a date for every diagnosis entry so that we can show a progressive medical record.