* stylistic adjustments to admin user table

co-authored by: Alexander Purr <purr@ub.uni-leipzig.de>
* re-adding reverse ordering from ref 16383
* dataTable footer search-inputs always with 100%
* set relative lang-file path
* prevent listener action on DataTables-buttons
** solve interference of theme.js and DataTables
** prevents screen freeze caused by theme.scroll.lock() via theme.toggleSidebar()