Issue 51 - Create Receipt page, display after pledge / bounty

This is a pull request that implements most of the functionality requested by [Issue 51](https://github.com/bountysource/frontend/issues/51).

Outstanding issues:

* Rewards cannot be currently be edited. There appears to be no API call available to retrieve reward details for a specific user/fundraiser/reward tuple; even if there was, the ID of the new resource isn't available to query with, as it is not returned from the payment system.
* The anonymous/public functionality cannot be currently edited for the same reason as above.
* Layout could use some tweaking.