query_exec should not require project and dataset arguments

the only two required fields in a bigquery query are the sql query and the billing project. The billing project will be the default project for non-fully-qualified table names in a query.

I should be able to do the following:
query_exec(billing_project='myproject', "select count(*) from publicdata:samples.shakespeare") 
but this doesn't work because a dataset and project are required. 

You might consider collapsing the project and billing project, since they are essentially identical, in which case leaving project as a required arg makes sense. But the dataset argument is not very useful -- it might make sense as an optional arg, but not as a required one.