WellState FIBO: Return Segment Vectors from report()

This commit extends class WellStateFullyImplictBlackoil to report
segment-related quantities as Opm::data::Segment objects (included
in Opm::data::WellRates objects).  All wells have at least a top
segment in the context of WellState FIBO, so there is a meaningful
value to report for each well.

We put the extraction of segment-related quantities into a new
helper function

    WellStateFullyImplicitBlackoil::reportSegmentResults()

to avoid cluttering up the body of report() more than absolutely
needed.

The primary use-case for this is assigning appropriate values to
items 8 through 11 of restart vector RSEG.  In turn, this will
enable restoring these quantities from a restart file.

CMakeLists_files.cmake

@@ -70,6 +70,7 @@ list (APPEND TEST_SOURCE_FILES
   tests/test_stoppedwells.cpp
   tests/test_relpermdiagnostics.cpp
   tests/test_norne_pvt.cpp
+  tests/test_wellstatefullyimplicitblackoil.cpp
   )
 
 if(MPI_FOUND)