EclipseWriter: get rid of the EclipseHandle monster

instead, the wrapper classes now call ERT directly, so it's easy to
see what a given class does. interestingly the amount of additional
code required is neglectible (or even negative).
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...
EclipseWriter: hide the copy constructor in the Eclipse* helper classes
EclipseWriter: rename 'outputTimeStepIdx_' to 'reportStepIdx_'

because that better expresses what this variable intends to
represent. Once the meaning of the currentTimeStep() method in
SimulatorTimer is settled we could also switch back to this one if it
is decided that it is the report step index...