flow_ebos: do not use (smart) pointers for opm-parser objects anymore
this patch also includes code to make FlowMainEbos more autonomous (i.e. it does not derive from FlowMainBase anymore). this allows more flexibility how and what stuff gets created. Note that this implies that parts of #947 are included here (in particular the grid initialization).
this is the companion PR for OPM/ewoms#102.
I've verified that the performance of `flow_ebos` did not regress for the Norne deck.
I think it should include all parts of #947 because all of them are bug fixes.