We should migrate github issues into redmine before disable github issue system.

When migrating an github issue, should
* create a corresponding issue in readmine
* record all information of the issue in redmine
* append comment at the end of the github issue like this: “Please, could you open a bug in redmine in future? We are in process of migrating all the issues to redmine and github issue won’t be available after August. The issue is migrated to xxx”. xxx is the link of corresponding redmine issue.
* close the github issue