Add dashboard page

Move content from users#show to dashboards#show.
dashboards#show only can see in myself.
Tweak user page design (in progress)
Merge pull request #117 from kmiyake/iss-115_create_dashboard_page

ダッシュボードページを作成する
check 'Add GitHub Issue' as default
Merge pull request #121 from shirakia/iss-121_default_check_to_github

issues#newかissues#editにおいて「Add Github Issue」が出現する時はデフォルトでチェック入り状態にする
bug fix: cannot comment
Merge pull request #123 from shirakia/iss-123_comment_bug

IssueへCommentできない