refactor(ui): work on issues mentioned by @steffen-weber

• admin-dashboard.php: add prepared statements, remove unused query
• admin-config.php: remove overescaping
• admin-tag.php: refactor regex, remove unused SQL escaping
• showjobs.php: remove unused lines
• admin-folder-create-form.html.twig: added trans keyword
• admin-folder-edit-form.html.twig: refactor quotes for HTML tags
• replace md5(...) with verbose strings in many files

EDIT: fix further issues