Refactor fetching lists of investigations

Fix #405 (closed)

Alright, so I've made a lot of progress. I'm using branch issue_185 for testing purposes.

The issues that remain are as follows:

ParcelTable needs access to parcels' investigations

The parcel table needs access to the parcels' investigations in order to display the "Beamline" and "Start date" columns, and to allow filtering parcels by beamline/start date.

Until now, this relied on all the ivnestigations being fetched. Again, ideally, we should only have to fetch the investigations of the parcels displayed in the table. So the idea would be to have a way to fetch a specific list of investigations by IDs, as Loïc suggested in icat-plus#191 (closed).