A const well state was passed to functions that were modifying it by
calling setALQ(). Now the setALQ() method is made non-const, mutable
references to the well state are passed where sensible. The getALQ()
method uses map::at() instead of map::operator[] and no longer modifies
current_alq_. With this, it is now easy to see which methods modify the
well state and which don't. The alq-related members in the
WellStateFullyImplicitBlackoil class are no longer 'mutable'-qualified.
Implements gas lift optimization for a single StandardWell. Support for
gas lift optimization for multi-segment wells, groups of wells and
networks is not implemented yet.
The keywords LIFTOPT, WLIFTOPT, and VFPPROD are used to supply parameters for
the optimization. Also adds support for summary output of liftgas
injection rate via keyword WGLIR.
