Migrate code and issue related to common util

[at15]

Related issues: https://github.com/dyweb/mos/issues/16

Since the common util code have been split to a new repository, it's time to migrate the issues to the new repository and change the usage of github.com/dyweb/Ayi/common/* to github.com/dyweb/gommon/*

• [x] xephon-b see https://github.com/xephonhq/xephon-b/pull/29
• [x] Ayi itself #68
• [x] issues in Ayi, the migrated one are labeled as transferred