Count instances that matches query

Property definitions

popcorn $ Repository :: count
	# Count instances that matches `query`
	fun count(query: nullable QUERY): Int is abstract
lib/popcorn/pop_repos.nit:186,2--187,50

popcorn $ MongoRepository :: count
	redef fun count(query) do
		return collection.count(query or else new JsonObject)
	end
lib/popcorn/pop_repos.nit:337,2--339,4