This commit makes the 'groupData()' function return a
map<string, Opm::data::GroupData>
object instead of a
map<string, Opm::data::GroupConstraints>
object. The 'GroupData' structure adds a level of indirection to
the current per-group summary quantities that are directly assigned
by the simulator. While here, also move the assignment of the
current group constraints/control values out to a separate helper
to reduce the body of the per-group loop in 'groupData()'.
This is in preparation of adding support for reporting group-level
production/injection guiderates (Gx[IP]GR) to the summary file.
5bb4321824