Switch condition interface to phase presence facility

Commit 4aa0eaf introduced density and viscosity evaluators into the
BlackoilPropsAdInterface that accepted an externally assignable
condition to distinguish saturated from unsaturated cases.  As a
result of a few low-level technical problems with that approach,
this commit changes those affected interfaces to use the black-oil
specific 'PhasePresence' facility of opm-core's commit a033329.

Update callers accordingly.