fix(tables): make headers sort buttons with aria-sort

[danieltruong]

Fixes sorting across the admin tables.

• Sortable column headers are now buttons, so they work from the keyboard. Each header sets aria-sort and shows an arrow for the active sort. For a sort on several fields, the header of the first field shows it. A column whose own value is a multi-field sort, such as Contacts Name (lastName,+firstName), is marked too.
• Sorting a column goes back to page 1.
• A keyword search keeps the current sort.
• Publishing or unpublishing documents keeps the current page. Deleting every row on the last page steps back one page.
• Days Remaining on Comment Periods is no longer sortable. It is computed and the API cannot sort on it.
• Group contacts keep their page and page size after loading.
• The search page no longer runs a search when only the sort is in the URL.

Tests: new specs for the table template, the sort helper, activity, comment periods, project documents, group contacts and search.