test_search_paid_app

https://github.com/mozilla/gaia-ui-tests/issues/561

## Precodition
1. Marketplace-dev app is installed on the test Firefox OS device.
2. Marketplace-dev app has been successfully launched.


## Steps to test
1. Do a blank search from the marketplace homepage
3. Click on Filter link in the header on the search results page
4. Choose the option to filter for "paid" apps and click "Apply"
5. Click on any of the search results

## Expected result:
[X] Search returns only paid apps.
[] Clicking on any of the search results loads the details page for that paid app.