vhnd_availability() changed to fluff

http://manage.dimagi.com/default.asp?129242#727747
@snopoke 

I emit ```received_on``` in this way, because I noticed in previous solution that:
when we don't have a owner_id in dict (which is returned by ```'vhnd_availability``` method), then we raised InvalidRow. When we have a owner_id, but we don't have filled vhnd_form, then we set to ```met_one``` VHND_NO image, and last case, when we have owner_id and we have a filled vhnd form, we don't do anything.

I group by ```received_on``` date, because I want to emit records which don't have filled forms, And in ```VhndAvailabilityCalc```,  I return ```0``` or ```1``` depending on if the ```case``` contain vhnd forms or not.

Is this make sense?