[scorecards] Make it more obvious how to filter Single Tier Councils by country (England/Scotland/Wales) on the homepage

[zarino]

CEUK have received feedback that people aren’t finding the England/Scotland/Wales country filter under "Advanced filters":

How can we make the country filters more obvious?

Would it help if we also considered this alongside #686 (allowing comparisons with "similar councils") and #611 (filtering District councils by metropolitan and non-metropolitan)?