Housing proposals

This is a big one. Mostly derived from the proposals of the campaign group [Generation Rent](http://generationrent.org) so I'd suggest that if some of the elements of the proposal sounds questionable, take a look at the GR manifesto first ;)

With this, I also wanted to trial having a section of "aims" at the top of the page, so readers can see at a glance, the general idea behind the policies in this area.