Sanity tests for Consumer Pages

This PR is for issue https://github.com/mozilla/marketplace-tests/issues/524

Tests are strengthened/modified, new tests added to address https://moztrap.mozilla.org/runtests/run/57/env/112/ list with sanity tests
I am confused by the fact that there are these specific locators here, and then the same elements (for the most part) are included in `footer_links_list` below. For example, `_privacy_policy_link_locator` targets the same element as the 4th item in `footer_links_list`. It would seem to me like you could get rid of one set or the other. Please take a look at the tests that use these and see if this duplication can be removed.