Should support parts parsing for plenum protocols

[aryehpro]

We should support the same functionality as the one that exists for committee meeting protocols (see source here).

This will be used by the knesset-data-pipelines project for parsing plenum meeting protocols (see issue here).

Code can and should be based on existing parts parsing from the knesset-data-django project (see source here)

[aryehpro]

@OriHoch I'm working on this, could you assign me?