Issues empty state

## What does this MR do?

Adds the empty state for the project, dashboard and group issues.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

### Filtered to show no issues (on group issues page in this case but also dashboard and projects)

![Screen_Shot_2016-11-08_at_20.55.56](/uploads/b598af4a8a5e2c9fbb859abf36e70e4b/Screen_Shot_2016-11-08_at_20.55.56.png)

### Project with no issues

![Screen_Shot_2016-11-08_at_20.57.08](/uploads/8f54fdf1b3101c46299249fa2944207d/Screen_Shot_2016-11-08_at_20.57.08.png)

![Screen_Shot_2016-11-08_at_20.57.17](/uploads/1d2d162e1d845dd05e945d8ebb1d2101/Screen_Shot_2016-11-08_at_20.57.17.png)

### Group with no projects with any issues

![Screen_Shot_2016-11-08_at_20.54.55](/uploads/f28dc2038839d5bda0eb37f37927d5db/Screen_Shot_2016-11-08_at_20.54.55.png)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #20840 

Closes #20850

See merge request !7309