Debouncing a setSearchTerm request causes strange behavior, because
it ends up making the original API request after the subsequent
actions. This has some odd side effects, like clearing out the filters
that were just set.

In order to work around this short term, I've added a "clearFilters"
flag which can be added to the setSearchTerm action.

Added the clearFilter option to the SearchBox, and updated
documentation.

I updated these tests because they were testing the wrong thing.

There are two side effects that occur as a result of setSearchTerm:
_udpateSearchResults
_makeSearchRequest

_udpateSearchResults is what we are debouncing, so we want to verify
whether that has run or not. Testing whether or not an API request
has been make is not a good way to test this, since _makeSearchRequest
is now always debounced.

In other words, we could call _udpateSearchResults 3 times in a row
and it will execute 3 times, but ultimately only one api call will be
made.