Default set current user to assignee select box

アサインユーザーにログインユーザーを初期セットする。
Merge pull request #388 from kmiyake/iss-120_default_set_current_user_to_assignee

Default set current user to assignee select box
Add close, reopen and comment feature
Merge pull request #391 from kmiyake/iss-161_feature_close_and_comment

Add close, reopen and comment feature
Update some gems
Fix test for updating rspec
Merge pull request #392 from kmiyake/iss-389_update_gems

Update some gems
Add feature of preview comment
Fix bug of showing comment list

コメントにmarkdown処理が適用されていない。
Merge pull request #393 from kmiyake/iss-390_feature_of_preview_comment

Add feature of preview comment
Use strong paramaters intead of raw params
Refactor code

検索関連の操作はscopeに定義する。
Add feature of continuing add issue

fix #380
Fix incorrect code
Include enabled_github paramater as part of issue_params
Add test and rename method
Merge pull request #394 from kmiyake/iss-380_feature_of_continuing_to_add_issue

Add feature of continuing to add issue