Proposal create

#### Story
> As a developer who's interested in applying for an RFP
> When I click on the proposal email call to action

The email doesn't appear to be a part of this story. @slicebo123 you were doing something related to email, but I don't think it's related to this. @rappo @juliangiuca can you confirm whether or not these email templates are part of this story?

> Then I am taken to a Proposal landing page
> And I can fill out my proposal information

![image](https://cloud.githubusercontent.com/assets/692632/3167919/e1201538-eb76-11e3-88b9-e356f57ed68d.png)

#### Acceptance
> The developer needs to be able to edit or delete their proposal before submitting, and cancel their proposal after submission

In the interest of MVP, this feature was left out. The form creates a Proposal which is immediately "submitted" the the RFP issuer.

> The developer should not be able to edit a submitted proposal

There isn't even a ProposalsController update action.

> The developer should be able to return to their proposal at any point in time (unless it's been deleted)

Once a developer creates a proposal, they will see it on the proposals tab:
![image](https://cloud.githubusercontent.com/assets/692632/3167935/43870b3c-eb77-11e3-8c88-820c697781cb.png)