header: remove unnecessary <div>
Revert user-profile preloading with jQuery

Due to constant problems and uselessness, this
reverts the commits 920b11d6bd and 1eca7f3b41.
comment preview: add display options

Enable the user to show the preview permanently or never.
correct SCSS import paths
restyle candidate and especially review page

Move stylings for candidates to new SCSS import file, using
a placeholder selector. Use these styles for review pages as
well. Improve existing styles for the 2 pages. Remove remai-
ning review list styling from review "view" SCSS.

Adjust review.php and candidate.php to new styling rules. Do
some minor code refactoring.

Also improve JS for review list and candidate list.
prettier styling for user list page
minor bug fix for review listing
change SCSS mixin to placeholder + extend
combine styles for user list and user item list

Apply the user list styles to the user item list as well.
Move them into a new separate SCSS import file, using a
placeholder selector. Adjust 'users/items.php' to the new
styling rules.
add AHK icon to index