Use common group tags for tag autocompletion

This applies the new stored/updated lists of common tags for each group
to the topic-tagging form, both for new submissions as well as editing
the tags on an existing one.

tildes/tildes/templates/intercooler/topic_tags_edit.jinja2

@@ -12,7 +12,7 @@
     data-ic-target="#sidebar .topic-tags"
     data-js-remove-on-success
 >
-  {{ topic_tagging(value=topic.tags|join(', '), auto_focus=True) }}
+  {{ topic_tagging(value=topic.tags|join(', '), auto_focus=True, autocomplete_options=topic.group.common_topic_tags) }}
   <div class="form-buttons">
     <button class="btn btn-primary" type="submit">Save tags</button>
     <button type="button" class="btn btn-link" data-js-cancel-button>Cancel</button>

tildes/tildes/templates/macros/forms.jinja2

@@ -16,7 +16,7 @@
   >{% if text %}{{ text }}{% endif %}</textarea>
 {% endmacro %}
 
-{% macro topic_tagging(value=None, auto_focus=False) %}
+{% macro topic_tagging(value=None, auto_focus=False, autocomplete_options=None) %}
   <div class="form-autocomplete form-group" data-js-autocomplete-container>
     <label class="form-label" for="tags">
       <span>Tags (optional, comma-separated)</span>
@@ -34,7 +34,7 @@
         spellcheck="false"
         name="query"
         placeholder='Tags (like "music, soundtrack, full album")'
-        data-js-autocomplete-input=""
+        data-js-autocomplete-input='{{ autocomplete_options|tojson if autocomplete_options }}'
         {% if value %} value="{{ value }}"{% endif %}
         {% if auto_focus %}data-js-auto-focus{% endif %}
       >

tildes/tildes/templates/new_topic.jinja2

@@ -52,7 +52,7 @@
       </div>
     </fieldset>
 
-    {{ topic_tagging() }}
+    {{ topic_tagging(autocomplete_options=group.common_topic_tags) }}
 
     <div class="form-buttons">
       <button type="submit" class="btn btn-primary">Post topic</button>