[Feature] Step-by-step input/output job snapshot, status and retrieval

[fmigneault]

Because of the multiple I/O format/conversion handling between WPS-REST, WPS-1/2, actual WPS XML requests and CWL package, it is hard to pinpoint the source of an error when one occurs.

Job object saved to db should provide, inputs_xml (values for WPS resquest, see #240), inputs_json (set after parsing of raw inputs and validation) and inputs_cwl (set before package execution) properties to get/set the inputs definition at any given execution step on top of the existing property for submitted inputs.
Idem for outputs.

When sending a request to /jobs/{id}/(inputs|outputs), the full details should be retrievable for each step using a query parameter to control all|cwl|wps|submit (default: submit to preserve current behaviour)

Note

Returned input values should consider masking according to #511

Adding this detail would help identify where a conversion did not occur correctly, or where an error was raised by looking at the last inputs/outputs section that had values and next that didn't have any. Another property Job.step should be added to directly running this interpretation mechanism and return a value identifying the last reached step. The step should be returned in JSON response of Job status.

relates to #221, #238, DAC-532