add confirmation flash when submission preferences are saved

securedrop/journalist_app/admin.py

@@ -59,6 +59,7 @@ def update_submission_preferences():
         form = SubmissionPreferencesForm()
         if form.validate_on_submit():
             # The UI prompt ("prevent") is the opposite of the setting ("allow"):
+            flash(gettext("Preferences saved."), "submission-preferences-success")
             value = not bool(request.form.get('prevent_document_uploads'))
             InstanceConfig.set('allow_document_uploads', value)
             return redirect(url_for('admin.manage_config'))

securedrop/journalist_templates/config.html

@@ -54,6 +54,7 @@ <h2>{{ gettext('Submission Preferences') }}</h2>
   <button type="submit" id="submit-submission-preferences">
     <i class="fas fa-pencil-alt"></i> {{ gettext('UPDATE SUBMISSION PREFERENCES') }}
   </button>
+  {% include 'submission_preferences_saved_flash.html' %}
 </form>
 
 {% endblock %}

securedrop/journalist_templates/logo_upload_flashed.html

@@ -1,4 +1,4 @@
-{# these are flashed messages for the logo upload file verifiaction #}
+{# these are flashed messages for the logo upload file verification #}
 {% with messages = get_flashed_messages(with_categories=True, category_filter=["logo-success", "logo-error"]) %}
   {% for category, message in messages %}
     {% set category_status = category[5:] %}

securedrop/journalist_templates/submission_preferences_saved_flash.html

@@ -0,0 +1,10 @@
+{# these are flashed messages for the logo upload file verifiaction #}
+{% with messages = get_flashed_messages(with_categories=True, category_filter=["submission-preferences-success"]) %}
+  {% for category, message in messages %}
+    {% set category_status = category[23:] %}
+      <div class="flash {{ category_status }}">
+        <img src="{{ url_for('static', filename='i/success_checkmark.png') }}" height="17" width="20">
+        {{ message }}
+      </div>
+  {% endfor %}
+{% endwith %}