Add :title as attribute for basic_topic

When we update the `<title>` after editing a topic, we should use the raw
`topic.title` as `topic.fancy_title` may contains some htmlentities and
will be displayed as is in the browser tab.

This fix the following issue:

> Incorrect HTML title after editing title/category of topic
> http://meta.discourse.org/t/incorrect-html-title-after-editing-title-category-of-topic/8136