Return user to summary page after clicking 'edit' and saving

When you edit a page, saving your changes should return you to the summary page.

The default flow is still to complete one page after another.

This commit add a URL parameter (`return_to_summary`). On the 'edit' links on the summary page it is set to `yes`.

When you view a page which has `?return_to_summary=yes` after the URL the button will say 'Save and return to summary' rather than 'Save and continue'. Clicking the button will do what the button says it does.

![screen shot 2014-10-22 at 13 17 02](https://cloud.githubusercontent.com/assets/355079/4735924/99cb009c-59e6-11e4-96e2-69e7ccdf8e2a.png)