Search form merge and country filter

This change is for https://www.pivotaltracker.com/story/show/36718601 and https://www.pivotaltracker.com/story/show/38329451.

Merges search & date change forms into one and adds measure filtering by country. This is pretty substantial change, I wouldn't rush this into production until we are sure that is how it should work. To me personally, separate forms were much more clear.

@tombye any chance you could look into frontend code changes?