Fix open issues count

Fixed #346
Merge pull request #351 from kmiyake/iss-346_show_my_open_issue_count

Fix open issues count
Extract to service object

Fixed #350

- Extract create comment method to GithubMediator
- Extract update comment method to GithubMediator
- Extract delete comment method to GithubMediator
Fix bug when open edit issue page

Githubオブジェクトが生成されていない
Merge pull request #354 from kmiyake/iss-350_extract_service_object

Extract Service Object