Added bookshelves to breadcrumbs

- Updated breadcrumb dropdown switchers and back-end sibling code to handle new breadcrumbs.
- Added breadcrumb view composer and EntityContext system to mangage
tracking if in the context of a bookshelf.

resources/views/shelves/list-item.blade.php

@@ -12,7 +12,7 @@
 <div class="entity-shelf-books grid third gap-y-xs entity-list-item-children">
     @foreach($shelf->books as $book)
         <div>
-            <a href="{{ $book->getUrl() }}" class="entity-chip text-book">
+            <a href="{{ $book->getUrl('?shelf=' . $shelf->id) }}" class="entity-chip text-book">
                 @icon('book')
                 {{ $book->name }}
             </a>