Add support for bookmark thumbnails (#721)

* Preview Image

* fix tests

* add test

* download preview image

* relative path

* gst

* details view

* fix tests

* Improve preview image styles

* Remove preview image URL from model

* Revert form changes

* update tests

* make it work in uwsgi

---------

Co-authored-by: Sascha Ißbrücker <sascha.issbruecker@gmail.com>

bookmarks/templates/settings/general.html

@@ -127,6 +127,15 @@
             <button class="btn mt-2" name="refresh_favicons">Refresh Favicons</button>
           {% endif %}
         </div>
+        <div class="form-group">
+          <label for="{{ form.enable_preview_images.id_for_label }}" class="form-checkbox">
+            {{ form.enable_preview_images }}
+            <i class="form-icon"></i> Enable Preview Images
+          </label>
+          <div class="form-input-hint">
+            Automatically loads preview images for bookmarked websites and displays them next to each bookmark.
+          </div>
+        </div>
         <div class="form-group">
           <label for="{{ form.web_archive_integration.id_for_label }}" class="form-label">Internet Archive
             integration</label>