Build corporate blog

closes #189 and #191 

This branch has:
* an awesome corporate blog (which can be written in markdown!)
* a twitter feed
* the ability to create an admin person who can write blogposts

At the moment you can only add an admin in the console, by doing:
* p = Person.find(1) (or whoever)
* p.add_role :admin
* p.save

You can then check if a person is admin by doing:
* p = Person.find(1)
* p.has_role? :admin

Further documentation on the rolify gem is here: https://github.com/EppO/rolify

I suggest we just do this for now, or maybe have one main admin for the whole site. The only advantage to being an admin at the moment is that you can blog. Maybe later it'll make sense to have an admin section where the admin users can be managed but I don't think that really matters at the moment.