Fix messages and strip html tags if needed.

#6346 

This PR fixes the messages so html tags are stripped besides those allowed. The issue happened since in themes based on ``os_basetheme`` we don't get a call to the function that originally fixed it, ``hwpi_basetheme_status_messages()``.

Output:
![selection_323](https://cloud.githubusercontent.com/assets/4497748/3505404/f9e23b6c-065d-11e4-9322-64039d317a9b.png)


Why not use theme item list?