structure betwen "RelatedAides" in levels 1-3 and "Breakdown" in level 0 not similar enough

[valevo]

• in level 0, in the field "Breakdown", references to guides are named "Link", while in other levels, they are named "link" (note upper- and lower-case "L") --> please make uniform
• the structure is different:
  • on levels 1-3, a relationship with another RG is given by (1) naming its title, (2) its location ("link") and (3) its relationship type with the other guide
  • on level 0 (the top level), the title of the other RG is in the "Title" field and there named list

--> these different structures aren't necessarily problematic, but difficult to meaningfully process
--> for now (to enable the front-end design we have agreed on), I'll have to make these different structures more similar (by flattening some of the hierarchies) (NB: this doesn't change the content of the YAML files)
--> please ensure that the way an individual RG is referenced is the same across all levels

[Maarten86]

I think I resolved the "Link" issues by making all instances lower-case. I think I also resolved the title-naming issue by removing "Title: " in level 0 and just naming the title instead, ending with a colon (just like in the level 1-3 research guides). As for the relationship type, this requires some internal discussion first.

[Maarten86]

I added rel_types too now, all "see also"