Parsing supplementation: adding generic parsing steps

[ErnestaP]

sources: loader.py, pipeline.py

• [x] https://github.com/cern-sis/issues-scoap3/issues/44
• [x] https://github.com/cern-sis/issues-scoap3/issues/45
• [x] https://github.com/cern-sis/issues-scoap3/issues/46
• [x] https://github.com/cern-sis/issues-scoap3/issues/47
• [x] https://github.com/cern-sis/issues-scoap3/issues/48
• [x] https://github.com/cern-sis/issues-scoap3/issues/52
• [x] https://github.com/cern-sis/issues-scoap3/issues/56
• [x] https://github.com/cern-sis/issues-scoap3/issues/57
• [x] https://github.com/cern-sis/issues-scoap3/issues/54
• [x] https://github.com/cern-sis/issues-scoap3/issues/58