Use ReactiveCaching to update external CI status asynchronously

See https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2055

Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NRémy Coutable <remy@rymai.me>

Adds mr id to changelog

This MR enables rendering of PlantUML diagrams in Asciidoc documents. To add a
PlantUML diagram all we need is to include a plantuml block like:

```
[plantuml, id="myDiagram", width="100px", height="100px"]
--
bob -> alice : ping
alice -> bob : pong
--
```

The plantuml block is substituted by an HTML img element with *src* pointing to
an external PlantUML server.

This MR also add a PlantUML integration section to the Administrator -> Settings
page to configure the PlantUML rendering service and to enable/disable it.

Closes: #17603

Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NRémy Coutable <remy@rymai.me>

Signed-off-by: NRémy Coutable <remy@rymai.me>

Centered alert text and prevented alert actions links from floating
right for viewports below medium width (992px)

Centered alert text stopped alert actions from floating right for viewports below medium width (992px)

Update styles to use correct screen width variable for max-width media query

Added unreleased changelog

Added class to alert links wrapper
Updated styles for new class, float alert links on larger screens

Fixed eslint failures

We should separate the idea of not finding anyone,
and the idea of against no one.

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7345/diffs#note_19994225

So that we don't have to check it again in somewhere else,
and we don't really need to know if it's presented as NONE

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7345/diffs#note_20123999

Thread:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7345/diffs#note_19707619