output writers: remove the state parameters from writeInit()

because as discussed with Atgeirr, this function should no longer
write the initial solution, it also does no longer need to know the
initial simulator state...
EclipseWriter: fold the writeSolution_() method back into writeTimeStep()

because this was the only caller...
EclipseWriter: remove unused method activeToGlobalCellData_()
EclipseWriter: write the summary file after each call to writeTimeStep()

this allows to interrupt a simulation and inspect the summary file
which was computed up to that point...
Merge pull request #558 from andlaus/EclipseWriter_refactor_writeInit_semantics

Eclipse writer refactor write init semantics
Merge pull request #559 from andlaus/EclipseWriter_fix_summary_output

Eclipse writer fix summary output