Added function grid_equal() to compare two UnstructuredGrid instances.
Renamed struct EclipseGrid -> struct EclipseWriterGrid to avoid conflict
with class in opm-parser.
ERT-601: Added GridManager() constructor which takes a Parser::EclipseGrid instance
Changed the data files used for testing:

1) Added RUNSPEC section
2) Replaces DEPTHZ keyword with TOPS keyword.
Merge pull request #581 from joakim-hove/GridManager-EclipseGrid-constructor

Grid manager eclipse grid constructor