Render 'back to search url' if coming from search or edit

[xmedr]

Overview

The "back to search" link in detail pages was only rendering if the link prior contains '/search/'. This allows it to also render if the link prior contains '/update/' for the edit page

Closes #67

Testing Instructions

• Search for a document (i.e. books - http://localhost:8000/books/search/ ) and select one of the results
• Confirm that the "back to search" link appears and works
• Back in the document detail page, click Edit, and then Cancel to return to the detail page from the edit page
• Again, confirm that the "back to search" link appears and works

[xmedr]

I'll probably be fine with one review from whoever has time!