Redesign pricing input

The prototype had a pricing matrix builder which we never carried across into the real app.

User research showed that this was both:
- Too complicated for some users to interact with
- Too simplistic for other user's pricing models

We have decided to replace it with a way of providing indicative pricing. This commit includes the design for the new pricing input.

It does not include:
- Updated copy required for this (will be done in the content repo)
- Validation rules that understand this new input

![screen shot 2014-10-08 at 09 07 00](https://cloud.githubusercontent.com/assets/355079/4555800/29f98b6e-4ec2-11e4-9629-c8cc6c6aba35.png)