Add support for PRIVATE flag in import and export (#505)

* Add support for PRIVATE attribute in import

* Add support for PRIVATE attribute in export

* Update import sync tests

bookmarks/templates/settings/general.html

@@ -144,6 +144,16 @@
         added and existing ones are updated.</p>
       <form method="post" enctype="multipart/form-data" action="{% url 'bookmarks:settings.import' %}">
         {% csrf_token %}
+        <div class="form-group">
+          <label for="import_map_private_flag" class="form-checkbox">
+            <input type="checkbox" id="import_map_private_flag" name="map_private_flag">
+            <i class="form-icon"></i> Import public bookmarks as shared
+          </label>
+          <div class="form-input-hint">
+            When importing bookmarks from a service that supports marking bookmarks as public or private (using the <code>PRIVATE</code> attribute), enabling this option will import all bookmarks that are marked as not private as shared bookmarks.
+            Otherwise, all bookmarks will be imported as private bookmarks.
+          </div>
+        </div>
         <div class="form-group">
           <div class="input-group col-8 col-md-12">
             <input class="form-input" type="file" name="import_file">
@@ -171,6 +181,10 @@
     <section class="content-area">
       <h2>Export</h2>
       <p>Export all bookmarks in Netscape HTML format.</p>
+      <p>
+        Note that exporting bookmark notes is currently not supported due to limitations of the format.
+        For proper backups please use a database backup as described in the documentation.
+      </p>
       <a class="btn btn-primary" href="{% url 'bookmarks:settings.export' %}">Download (.html)</a>
       {% if export_error %}
         <div class="has-error">