Add disable gravatar option

conf/app.ini

@@ -166,6 +166,7 @@ SESSION_ID_HASHKEY =
 [picture]
 ; The place to picture data, either "server" or "qiniu", default is "server"
 SERVICE = server
+DISABLE_GRAVATAR = false
 
 [log]
 ; Either "console", "file", "conn", "smtp" or "database", default is "console"