Remove eclipse grid parser

This PR removes all traces of EclipseGridParser (kind of a 'Damnatio memoriae' for code).

This PR is _not_ intended to be merged immediately but only after #579 and the follow-ups for dune-cornerpoint and opm-{porsol,upscaling,benchmarks,verteq,upscaling} have been merged. (the latter depend on #579 and the "move dune-cornerpoint to new parser" PRs so they have not yet been pushed to github yet but they already lurk on my harddisk). The point in this PR is to give you a glimpse on what's coming and what I will base my multi-PVT stuff on. (I _really_ do not want to do this for the old parser in addition to the new one just to throw this work away two weeks later.)