This commit adds support for saving and restoring cumulative
production quantities like WOPTH, GWPTH, FGPTH, GGITH, and WWITH.
While here, also cater to the case of wells alternating between
injecting gas and injecting water. This means that we'll save and
restore cumulative gas/water injection for all injectors,
irrespective of current injecting phase.
Update unit tests accordingly.