Close T1010

This takes care of current limitations:
- duplicated elements are stored as list (and no longer dropped)
- drop extra namespace in key names
- it's generic

Close T1131

Related T1131

As in making sure they are checking the right failures.

Related T1010#20870

Multiple things went wrong, which explains the issue in production:

- the internal representation is expected to be a tuple for the
  post (not an HttpResponse instance)

- the tests were failing on the expected bad status for the wrong
  reason (bad deposit status was used, 'ready' instead of 'partial',
  an update can only take place on 'partial' deposit)

- the tests were differents but tested the same endpoint either
  way (only put was called)

Related P279
Related T1010#20869
Related T1010#20870

Related T1034

Related T565

Related T565

Related T882