Category and Tag Description and SEO fix

Hi,
the details of what I've done is at the commits.
* show cat & tag description on archive pages (if entered)
* change the use of headlines (blog title and post title)

One small to do you you (I don't know 100% how it works in wordpress) add a translation for the "Currently browsing: " string I've add. (For German I can translate it If you like).

I hope this will okay, for [my needs](http://www.iamyourfather.de/kategorie/buchempfehlung) it works fine.