Add some HTML5 tags to RICHTEXT_ALLOWED_TAGS
Add some HTML5 tags to RICHTEXT_ALLOWED_TAGS

Hi,

This patch adds the following tags to RICHTEXT_ALLOWED_TAGS:

* article
* aside
* figure
* caption
* header
* footer
* nav
* section

... all of which are becoming increasingly common, and should all be safe to allow.

Thanks!
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