Post to the API when moving folders and templates

This commit adds logic to:
- take the list of selected folders and templates
- split it into two lists (of folders and templates)
- `POST` that data to the API, to effect the movement of said folders
  and templates

I’ve tried to architect it in such a way that we can easily add more
template ‘operations’ in the future, as we add more forms to the choose
template page.

app/templates/components/page-footer.html

@@ -16,6 +16,8 @@
       <button
         type="submit"
         class="button{% if destructive %}-destructive{% endif %}"
+        {% if button_name %}name="{{ button_name }}"{% endif %}
+        {% if button_value %}value="{{ button_value }}"{% endif %}
       >
         {{- button_text -}}
       </button>