Prepare for room v3+, misc bugfixes

vona/client/__init__.py

@@ -621,7 +621,7 @@ async def url_preview():
 @client.route("/_matrix/client/v1/media/preview_url")
 async def media_preview():
 	response = send_file(config.cat)
-	response.headers["Content-Disposition"] = f'inline; filename="cat.jpg"'
+	response.headers["Content-Disposition"] = 'inline; filename="cat.jpg"'
 	response.headers["Content-Type"] = "image/jpg"
 	return response