Ecl2df

Bugfix release:
* Make --stackdates work as intended for ecl2csv grid
* Support time interpolations beyond year 2262 in summary
* Do not remove completions from multiple wells into the same cells in compdat.

Bugfixes:
* Fix crash in fipreports on rogue Eclipse output

Improvements:
* Support OPM flow PRT output in fipreports.

Changes:
* The column ACCURACY in the dataframe from the equil module has been renamed to OIP_INIT

Improvements:
* The grid module outputs Z_MIN and Z_MAX also for every cell row.
* lyr files (which links zone names to k-layers) supports colour metadata.

Installation:
* ert is now an optional dependency, and will no longer be installed by default.

* Compatibility with OPM 2021.04
* When parsing WELOPEN with lumped connections, `ecl2df.compdat` will fail hard instead of returning erroneous data.

* Refactor zonemap parsing for use in other projects
* Use NaN in dataframes where libecl grid output otherwise gives 1e-20.

Bugfix for ERT integration of csv2ecl summary.

The command line API for csv2ecl summary was not compatible with the ERT integration and has been changed. The ECLBASE argument is now supplied as --output, similar to the other csv2ecl subcommands.

Also add possibility for csv2ecl to write to subdirectories.