Extends PR #2824 to include support for GLIFTOPT (item 2, maximum lift
gas supply for a group) and group production constraints.
The optimization is split into two phases. First the wells are optimized
separately (as in PR #2824). In this phase LIFTOPT and WLIFTOPT constraints
(e.g. maxmimum lift gas injection for a well, minimum economic gradient) are
considered together with well production constraints.
Then, in the next phase the wells are optimized in groups. Here, the ALQ
distribution from the first phase is used as a starting point. If a group
has any production rate constraints, and/or a limit on its total rate of
lift gas supply, lift gas is redistributed to the wells that gain the most
benefit from it by considering which wells that currently has the largest
weighted incremental gradient (i.e. increase in oil rate compared to
increase in ALQ).
