When running test in opm-parser, this never showed up as a problem since
Equil.hpp seems to be always included after <vector> is included (either
directly or by including other files). However, this can become a
problem when using opm-parser in other projects (eg, sunbeam)
Introduces Equil, a thin storage class for 'EQUIL' derived information,
accessible through EclipseState.
Previously this was handled through "raw" deck access, provided by
EquilWrapper. The interface for Equil has been derived from the
EquilWrapper, but they're to be seen as different entities altogether.
More importantly, Equil is owned by EclipseState, not some stand-alone
Deck reading unit.
