Add terms on client side.

I know that this should be proposed as a patch in mozilla-central.
I put it here to work on the patch and then I will make the appropriate patch to mozcentral.

 - [x] HTML / Ajax term loader based on the Accept Language of the browser (given back by loop-server)
 - [x] Extract ToS from legal-docs using grunt and bower.
Eventually, this should have cache friendly (busting) URLs.