Search filter api again fix

Supercedes @tx2z's search filter api PR:  https://github.com/mozilla/kuma/pull/2399

@tx2z:  I fixed merge conflicts...I think.  Can you test and make sure your work is as how you remember it?

@stephaniehobson:  Can you look at the CSS here and let @tx2z know if we should make updates?


@ubernostrum - This is the weird part causing the test failure. I don't know why this line is an addition. This file has been removed, hasn't it? In any case, this line isn't in the master branch of this test file.