* 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
* Improve overview of accounts in admin UI
- Display suspended status, role, last activity and IP prominently
- Default to showing local accounts
- Default to not showing suspended accounts
* Remove unused strings
* Fix tests
* Allow filtering accounts by IP mask
Deleted users are technically suspended, but the code displaying their status
in the admin interface was broken and displayed a javascript object holding
translations of the possible user roles instead.
