Add gravity() method.
Moved some calculations to computeExplicitData() method.
Fix initialization issue with gpot_.
Removed qs from the set of primary variables.
Merge remote-tracking branch 'bska/master'
Temporarily ignore viscosity derivatives.
Clarify some variables' purposes.
Merge branch 'master' into fully-implicit
Renamed ImplicitBOStep -> FullyImplicitBlackoilSolver.
Added (empty) implementation file.
Class FullyImplicitBlackoilSolver is no longer a template.
Moved implementation to .cpp file.
Implement residualNorm()

This is a prerequisite to having a working Newton loop.
Merge remote-tracking branch 'atgeirr/fully-implicit' into fully-implicit

Conflicts:
	opm/autodiff/ImplicitBOStep.hpp
Implement residualNorm() for reservoir part.

This is a prerequisite to having a working Newton loop.

This is a forward-port of commit 604f866.
Added simulator class for fully implicit blackoil.
Merge remote-tracking branch 'atgeirr/fully-implicit' into fully-implicit