Celus-pycounter

* Fix proprietary_id for BR1 and BR2

* Forked from original project
* Use poetry for dependency management

* COUNTER 3 support removed (was at EOL in 2014).
* CounterReport no longer has .year attribute (doesn't make sense for part or multi
year reports, and wasn't on COUNTER 5 reports in pycounter 2.0)
* Dropped support for python 2 and 3.5. Now supports only python 3.6+
* Request SUSHI server status (COUNTER 5 only at the moment)

* Better handling of report JR2 [Stepan Henek]

* fix a missed place with too-strict date handling

* less strict date handling in Begin/End date strings to allow working with
badly-formatted reports that exist in the wild.