* Move .back-button inline styles to CSS file

All occurrences of the back-button CSS class used the same inline
CSS rules, so moved them over to the CSS file

* Fix “Add new domain block” button using inline CSS

* Replace common pattern of inline-styled button boxes by a CSS class

In particular, switching from `float: left/right` to a flexbox with
`justify-content: space-between`. This implied changing the order of
a few HTML tags and adding an empty `div` in one case.

Also removed a `margin-bottom` rule that wasn't needed due to the
margins of surrounding elements.

* Move account admin view inline CSS to CSS file

* Allow to show a specific status in the admin interface

* Let the front-end know the current account is a moderator

* Add admin links to status and account menus

If the current logged-in user is an admin, add quick links to the admin
interface in account and toot dropdown menu. Suggestion by @ashkitten

* Use @statuses.first instead of @statuses[0]

* Improve design of account statuses admin UI (consistent with reports)

* Make account moderation notes look consistent with report notes

* i18n-tasks remove-unused

* Fix code style issues

* Fix tests

* Improve admin page

* Fix test

* Add spec

* Improve select style