Claim Assosciated pdf

- [x] Background pdf (generate_pdf! can be called on a claim in any background process)
- [x] Adds a meta refresh page(5 seconds) for use when pdf has yet to be generated
- [x] Associate a pdf with a claim model
- [x] Carrierwave config. Expiry URL AWS setting needs tetsing!

![screen shot 2014-12-04 at 14 43 44](https://cloud.githubusercontent.com/assets/1006365/5300083/d3e9b502-7bc4-11e4-9841-4c9b1531f0ae.png)

I agree with you, @stevegraham. I'm not sure what would be clearer, though. `ensure_pdf_exists` or `generate_pdf_if_needed`? I don't love either of those, though.