Bug 1055048: Move legal docs handling to separate app.

* Add generic view for legal docs.
* Convert privacy app to use new legal docs utils.
It appears that some of this markup manipulation is specific to the output expected on the Privacy pages ([example](https://www.mozilla.org/en-US/privacy/websites/)). I foolishly assumed that this was dumping the entire contents of the page, but it is doing some magic, only grabbing ```<p>```, ```<ul>```, & ```<hr>``` tags.

It is also putting any P tags before the first ```<hX>``` tag into the ```<header>``` section. This works for the privacy docs, but is too limited for general use.

I wonder if this is something the privacy app can do on it's own?