Cache update

f? 

The only issue is if you do a 'Clear Cache' then  a 'Download All Documents' without viewing the home page again, it only caches the default topics (there's 4 of them) from the front page. This is because it looks in the database for 'topics:' to find which subtopics it should send off to kitsune to cache.
Just do `$scope.updateCache = updateCache;`.