feat: schema validation, add choice + zeroOrMore for DataObjectGroup (closes #35)

--HG--
branch : seda21
5 jobs for topic/seda21/choice_zero in 2 minutes and 12 seconds (queued for 33 minutes and 35 seconds)
Name Stage Failure
failed
flake8 Lint
ERROR: InvocationError for command /builds/cubicweb/cubes/seda/.tox/flake8/bin/flake8 . (exited with code 1)
___________________________________ summary ____________________________________
ERROR: flake8: commands failed
Uploading artifacts for failed job
Uploading artifacts...
gl-code-quality-report.json: found 1 matching files and directories

Uploading artifacts as "codequality" to coordinator... ok
id=427141 responseStatus=201 Created token=qb7HCaTt
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1