Style Select2 widgets and remove wrong filter form class
Style Select2 widgets and remove wrong filter form class

This fixes #1264 by removing `class="form-inline"` from filter form
definition (which helped getting a proper form size in the sidebar),
and by adding attributes (SIDEBAR_DAL_WIDTH) to the Select2 widgets.

swcarpentry/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,swcarpentry/amy,pbanaszkiewicz/amy,swcarpentry/amy