Bibcheck: Adds check_nations plugin

* adds flatten_list and has_field to utils.py

* adds the bibcheck_task rule to rule.cfg and rule.cfg to the
  Makefile

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
Bibcheck: Corrects general behavior of check_nations plugin

* Rework due to misunderstanding of desired behavior of
  check_nations.py

* Removal of unnecessary function in utils.py

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
Bibcheck: adds scenarios for human eyeballing

* Reworks the find_nations method in check_nations.py to consider
  more scenarios which require a human check

* removes rules.cfg

Signed-off-by: Martin Vesper <martin.vesper@cern.ch>
Merge branch 'check_nations_bibcheck_plugin' of https://github.com/mvesper/scoap3 into mvesper-check_nations_bibcheck_plugin

Conflicts:
	Makefile
	utils.py
Merge branch 'mvesper-check_nations_bibcheck_plugin'