On the issue dashboard add a way to create a new issue

Dev: https://dev.gitlab.org/gitlab/gitlabhq/issues/2390

On https://dev.gitlab.org/dashboard/issues?milestone_id=&scope=all&sort=created_desc&state=opened&utf8=%E2%9C%93&assignee_id=26&author_id=&milestone_title=

@sytse

1. Make the repo link on the left link to /issues instead of the repo root
2. Replace the Show all on the right with a 'New issue' link

/cc @dzaporozhets @sytses @JobV