Fix todos page mobile viewport layout

## What does this MR do?
Fixes the todos page mobile viewport layout

## Are there points in the code the reviewer needs to double check?
Shouldn't be any 👍 

## Why was this MR needed?
Improve GitLab usability on mobile devices

## Screenshots (if relevant)
Before:
![Simulator_Screen_Shot_Sep_13__2016__11.30.19_AM](/uploads/7053a1bb1fca6238c5f86d671bf96ff0/Simulator_Screen_Shot_Sep_13__2016__11.30.19_AM.png)

After:
![Simulator_Screen_Shot_Sep_13__2016__11.30.04_AM](/uploads/a30921c1a1118655b547977872e8e1c7/Simulator_Screen_Shot_Sep_13__2016__11.30.04_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22097

See merge request !6325