Add bookmark sharing (#311)

* Allow marking bookmarks as shared

* Add basic share view

* Ensure tag names in tag cloud are unique

* Filter shared bookmarks by user

* Add link for filtering by user

* Prevent n+1 queries when rendering bookmark list

* Prevent empty query params in return URL

* Fix user select template tag name

* Create shared bookmarks through API

* List shared bookmarks through API

* Show bookmark suggestions for shared view

* Show unique tags in search suggestions

* Sort user options

* Add bookmark sharing feature flag

* Add test for share setting default

* Simplify settings view

bookmarks/templates/bookmarks/shared.html

@@ -0,0 +1,48 @@
+{% extends "bookmarks/layout.html" %}
+{% load static %}
+{% load shared %}
+{% load bookmarks %}
+
+{% block content %}
+
+    <div class="bookmarks-page columns">
+
+        {# Bookmark list #}
+        <section class="content-area column col-8 col-md-12">
+            <div class="content-area-header">
+                <h2>Shared bookmarks</h2>
+                <div class="spacer"></div>
+                {% bookmark_search filters tags mode='shared' %}
+            </div>
+
+            <form class="bookmark-actions" action="{% url 'bookmarks:action' %}?return_url={{ return_url }}"
+                  method="post">
+                {% csrf_token %}
+
+                {% if empty %}
+                    {% include 'bookmarks/empty_bookmarks.html' %}
+                {% else %}
+                    {% bookmark_list bookmarks return_url link_target %}
+                {% endif %}
+            </form>
+        </section>
+
+        {# Filters #}
+        <section class="content-area column col-4 hide-md">
+            <div class="content-area-header">
+                <h2>User</h2>
+            </div>
+            <div>
+                {% user_select filters users %}
+                <br>
+            </div>
+            <div class="content-area-header">
+                <h2>Tags</h2>
+            </div>
+            {% tag_cloud tags %}
+        </section>
+    </div>
+
+    <script src="{% static "bundle.js" %}"></script>
+    <script src="{% static "shared.js" %}"></script>
+{% endblock %}