Forms auto-populate data when possible

Trello: https://trello.com/c/AqwU4lJB/64-announcement-pitch-forms-are-auto-populated-when-possible

If a user navigates to a form from a client or announcement specific view, the form selection box is auto-populated with the relevant data. If the user navigates to a form from a generic view, the form selection box contains all possible data options.

![auto-populate](https://cloud.githubusercontent.com/assets/4560985/5284569/2a1ad772-7ae3-11e4-86e6-9c3cba83d9e2.gif)

use `new_client_announcement_path(@client)`