Encounter transaction API changes

These changes contain the API for "Load all encounters transactions by day (LongVisit)" from http://notes.openmrs.org/Design-Forum-2013-11-11. There has been few changes made to the current EncounterTransaction contract.

* Removed the EncounterTransactionResponse and using the EncounterTransaction for both request and response.
* Instead of ConceptUUID using a Concept object with { uuid, name} 
* Changed diagnosis so that concept name and uuid are in the response. It has been changed from from
```
	 {
                "order": "SECONDARY",
                "existingObs": "646b7a72-a541-4964-992e-a75a5459d3db",
		"diagnosis": "ConceptUUID:130651AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
                "certainty": "CONFIRMED"
       }
```
to
```
	 {
                "order": "SECONDARY",
                "existingObs": "646b7a72-a541-4964-992e-a75a5459d3db",
                "freeTextAnswer": null,
                "codedAnswer": {
                    "uuid": "140399AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
                    "name": "Fetal death"
                },
                "certainty": "CONFIRMED"
         }
```