added hoverstate on buttons, plus added spacing to make them more square when only the arrows are visible

- Improve isInViewport impementation to be robust.
- Autoscroll is now a status indicator instead of toggle button
- Scrolling build log enables autoscroll itself when scrolled to bottom.

- Improve isInViewport impementation to be robust.
- Autoscroll is now a status indicator instead of toggle button
- Scrolling build log enables autoscroll itself when scrolled to bottom.

Display error code for U2F errors

See merge request !7305

Apply margin on alert banners only when there is one or more alerts

## What does this MR do?

Fixes extra margin added to all pages by !8151

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

## Why was this MR needed?

## Screenshots (if relevant)

![screenshot](https://gitlab.com/gitlab-org/gitlab-ce/uploads/f8804454e82a61246d10fa026605fbb3/Screen_Shot_2016-12-19_at_2.04.42_PM.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 #25835

See merge request !8209

Rename SlackNotificationService back to SlackService

## What does this MR do?

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8191#note_20310845

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/25843

/cc @yorickpeterse @stanhu @smcgivern @felipe_artur @ayufan

See merge request !8208