Fix dependency on jinja2

Delay the import of ConsentResource, so that we can get away without jinja2 if
people don't have the consent resource enabled.

Fixes #3259

synapse/app/homeserver.py

@@ -41,7 +41,6 @@ from synapse.python_dependencies import CONDITIONAL_REQUIREMENTS, \
 from synapse.replication.http import ReplicationRestResource, REPLICATION_PREFIX
 from synapse.replication.tcp.resource import ReplicationStreamProtocolFactory
 from synapse.rest import ClientRestResource
-from synapse.rest.consent.consent_resource import ConsentResource
 from synapse.rest.key.v1.server_key_resource import LocalKey
 from synapse.rest.key.v2 import KeyApiV2Resource
 from synapse.rest.media.v0.content_repository import ContentRepoResource
@@ -186,6 +185,7 @@ class SynapseHomeServer(HomeServer):
             })
 
         if name == "consent":
+            from synapse.rest.consent.consent_resource import ConsentResource
             consent_resource = ConsentResource(self)
             if compress:
                 consent_resource = gz_wrap(consent_resource)