Perform database changes review to support integration of #711

Changes:
- Add 'antivirus_enabled' variable to make it possible to enable/disable the functionality via UI
- Edit the set of 'antivirus' variables to enable type checking on the configuration of the ClamD endpoint

backend/globaleaks/models/config_desc.py

@@ -127,7 +127,9 @@ class Bool(Item):
     'version_db': Int(default=DATABASE_VERSION),
     'wizard_done': Bool(default=False),
     'uuid': Unicode(default=uuid4),
-    'url_file_analysis': Unicode(default='http://localhost:3000/api/v1/scan'),
+    'antivirus_enable': Bool(default=False),
+    'antivirus_clamd_ip': Unicode(default='127.0.0.1'),
+    'antivirus_clamd_port': Int(default=3301),
     'max_msg_external_to_whistle': Int(default=1),
     'max_msg_external_to_whistle_not_aff': Int(default=1),
     'external_organization_activation': Bool(default=True),