add 800x600 thumbnails to make vector look prettier (and anyone else who likes big thumbnails)

synapse/config/repository.py

@@ -97,4 +97,7 @@ class ContentRepositoryConfig(Config):
         - width: 640
           height: 480
           method: scale
+        - width: 800
+          height: 600
+          method: scale
         """ % locals()