Make BlackoilPropsAdInterface pure virtual again.

Done by adding (throwing) implementation to BlackoilPropsAd class.
Merge pull request #95 from atgeirr/pure-virtual

Make BlackoilPropsAdInterface pure virtual again.
Using well_controls_well_is_open() function
Merge pull request #96 from joakim-hove/well-controls-open-close

Using well_controls_well_is_open() function