TRUNK-4109: Get observations by accession number

org.openmrs.api.ObsService#getObservations and
org.openmrs.api.ObsService#getObservationCount are now overloaded to support
specification of accession number.
If specified, only observations (or their count) with matching accession
number are returned.

See https://issues.openmrs.org/browse/TRUNK-4109

Unit tests for org.openmrs.api.ObsService#getObservations and
org.openmrs.api.ObsService#getObservationCount now use the new
(and most general) methods.
Merge pull request #963 from vencik/master

TRUNK-4109: Get observations by accession number
TRUNK-4315: Validate on client side (javascript)

Decided to validate on client side because on server side calling provider.getName()
when person is set will return person's full name and so it is not possible to tell if
this was set on the client side.

TRUNK-4315 - Removed commented out code

TRUNK-4315 - Ammended method for checking whether person or provider name is provided

TRUNK-4315: Added a span tag to hold error message from both client and server