[WIP] @1aurabrown => Switch View

I'm holding off on calling this "done" because of this (serious) problem with our testing suite: https://github.com/artsy/eidolon/issues/52

However, it's in an OK place to start a code review. 

Also I added in an Objective-C category taken from eigen. I'll probably swiftify it at some point. 
hah, it's like you missed the entire discussion between me and laura in chat about not doing this on buttons :P