Change to Comunica as a datasource

[pietercolpaert]

Right now, the data is fetched by individual classes resolving data using LDFetch

As an alternative, and from the moment comunica/comunica#473 is merged into master in Comunica, we must try to use this as a back-end.

To do:

• Refactor Comunica to support custom hypermedia forms Refactor source type handling comunica/comunica#473
• Add Tree ontology and tile referencing into Comunica as an actor
• Add the Linked Connections departureTimeQuery search form into Comunica as an actor
• Add an alternate data fetching strategies through Comunica

The ultimate goal is that we only configure Planner.js with 1 catalog, and that it knows where to fetch all the right datasets on the fly.