Implement UI theme colors.

web/templates/channel.html

@@ -29,6 +29,7 @@
   <div id="edit_mention_tab"></div>
   <div id="get_link_modal"></div>
   <div id="user_settings_modal"></div>
+  <div id="import_theme_modal"></div>
   <div id="team_settings_modal"></div>
   <div id="invite_member_modal"></div>
   <div id="edit_channel_modal"></div>