Option to disable single search result redirect

Adding back the settings option to enable / disable the redirect to product page on single search result based on code from the [original pull request](https://github.com/woothemes/woocommerce/pull/609), though I changed it to default to enabled. The change also adds two language strings, “Product Search” as a title, and “Redirect to the product page on a single matching search result”.

It looks like:

![image](https://f.cloud.github.com/assets/517889/281079/13a7a0fc-916e-11e2-9f45-4d036510f03b.png)

I added it back because in my WooCommerce implementation, I customized the search results page to have more than just the product results, so even if only one product is matched, I still want the results page to show up. I am guessing there are others who could use that option also.