plenum scraping should move to knesset-data

[OriHoch]

it is very similar to committee meeting scraping and protocol parsing

todo

• add the low-level code to knesset-data-python
  • the code that fetches the list of plenum meetings + parses the documents and returns protocol parts
• add the data as part of the datapackage in knesset-data-datapackage
• update relevant DB models in knesset-data-django

corresponding open knesset code

• https://github.com/hasadna/Open-Knesset/blob/master/plenum/management/commands/parse_plenum_protocols.py