Add missing items-list class (as per mockup)

src/templates/bookmarks_list.html

 <a href="#" class="rooms-toggle bookmarks-toggle" title="{{{o.desc_bookmarks}}}">
     <span class="fa {[ if (o.toggle_state === o._converse.OPENED) { ]} fa-caret-down {[ } else { ]} fa-caret-right {[ } ]}">
     </span> {{{o.label_bookmarks}}}</a>
-<div class="bookmarks rooms-list {[ if (o.toggle_state !== o._converse.OPENED) { ]} hidden {[ } ]}"></div>
+<div class="items-list bookmarks rooms-list {[ if (o.toggle_state !== o._converse.OPENED) { ]} hidden {[ } ]}"></div>

src/templates/rooms_list.html

 <a href="#" class="rooms-toggle open-rooms-toggle" title="{{{o.desc_rooms}}}">
     <span class="fa {[ if (o.toggle_state === o._converse.OPENED) { ]} fa-caret-down {[ } else { ]} fa-caret-right {[ } ]}">
     </span> {{{o.label_rooms}}}</a>
-<div class="rooms-list open-rooms-list"></div>
+<div class="items-list rooms-list open-rooms-list"></div>