added method to retrieve a ClinicalRecord that belongs to a specific Patient

Signed-off-by: Luca Lianas <lianas@crs4.it>
added /ehr/get to DBService REST API

Signed-off-by: Luca Lianas <lianas@crs4.it>
updated documentation

Signed-off-by: Luca Lianas <lianas@crs4.it>
Merge branch 'feature_121' into develop

close #121