Rights check on RetrieveCorpus

Closes #1101 (closed)

• Rewrote the API description
• Added help_text on fields whose meanings are non-trivial
• Fixed two RuntimeWarnings related to missing timezones on datetimes during unit test execution
• Added missing unit tests

requested review from @babadie

assigned to @erwanrouchet

added 11 commits

• 7b422d68...98af729a - 10 commits from branch master
• c315f33f - Rights check on RetrieveCorpus

Compare with previous version

mentioned in commit a34deff0

merged