Catch itegrity errors and return 400.

When creating or updating an organisation an itegrity error is raise if the name is already used.
This change adds a new error handler for the organisation to catch the named unique index and return a 400 with a sensible message.
We have an other error handler for unique service names which was caught in the error handler for all blueprints. A new error handler for the service_blueprint has been created for catch those specific unique constraints.
This is a nice way to encapulate the specific errors for a specific blueprint.

tests/app/organisation/test_rest.py

@@ -1,6 +1,3 @@
-import pytest
-
-from app.errors import InvalidRequest
 from app.models import Organisation
 from app.dao.organisation_dao import dao_add_service_to_organisation
 from tests.app.db import create_organisation, create_service
@@ -62,17 +59,16 @@ def test_post_create_organisation_existing_name_raises_400(admin_request, sample
         'active': True
     }
 
-    with pytest.raises(InvalidRequest) as e:
-        admin_request.post(
-            'organisation.create_organisation',
-            _data=data,
-            _expected_status=400
-        )
+    response = admin_request.post(
+        'organisation.create_organisation',
+        _data=data,
+        _expected_status=400
+    )
 
     organisation = Organisation.query.all()
 
     assert len(organisation) == 1
-    assert 'Organisation name already exists' in str(e.value)
+    assert response['message'] == 'Organisation name already exists'
 
 
 def test_post_create_organisation_with_missing_name_gives_validation_error(admin_request, notify_db_session):
@@ -114,22 +110,21 @@ def test_post_update_organisation_updates_fields(admin_request, notify_db_sessio
 
 
 def test_post_update_organisation_raises_400_on_existing_org_name(
-        admin_request, notify_db_session, sample_organisation):
+        admin_request, sample_organisation):
     org = create_organisation()
     data = {
         'name': sample_organisation.name,
         'active': False
     }
 
-    with pytest.raises(expected_exception=InvalidRequest) as e:
-        admin_request.post(
-            'organisation.update_organisation',
-            _data=data,
-            organisation_id=org.id,
-            _expected_status=400
-        )
+    response = admin_request.post(
+        'organisation.update_organisation',
+        _data=data,
+        organisation_id=org.id,
+        _expected_status=400
+    )
 
-    assert 'Organisation name already exists' in str(e.value)
+    assert response['message'] == 'Organisation name already exists'
 
 
 def test_post_update_organisation_gives_404_status_if_org_does_not_exist(admin_request, notify_db_session):