Fixes to the homepage and searchbar

Describe the bug

[x] Fix the defaults for the price filters should be null, rather than zero
[x] Fix the "Not Recommended" button on recommended listings take you to the listing, rather than greying out the card as expected
[x] Change the behaviour of updating filters to either apply automatically on search, or through some graphical indicator if that's easier
[x] And the spinner for low loading

Relates: #272