Feature of Synchronizing with the Github

Timecard上に存在しないGithubチケットのみ保存していく
Fix undesirable code

* Fix indent
* Remove don't need condition
* Extract hard code of convert status process
Fix logic of setting assignee
Add test
Merge pull request #309 from kmiyake/iss-304_feature_of_synchronizing_github

Feature of Synchronizing with the Github