Update models and relationships

[elpoelma]

This PR includes a complete revisal/update of all ember-data models. It includes the removal of models and relationships, the addition of missing models and relationships and ensuring the inverse field is always explicitly set (in prepreration for emberjs/data#8115).
Specifically, it includes the removal of the following ember-data models:

• task-solution
• task
• tasklist-solution
• tasklist
• versioned-agenda

And the removal of the following relationships:

• realisatie from besluit
• versioned-agendas, versioned-notulen, versioned-besluiten-lijsten and versioned-behandelingen from document-container
• replaced versioned-agenda model type by agenda in published-resource
• replaced versioned-agenda model type by agenda in signed-resource

The addition of the following models:

• beleidsdomein-code
• lidmaatschap
• lijsttype
• tijdsinterval
• werkingsgebied

Additionally, this PR also introduces spacing in some models to make them clearer and more readable.
To be tested in combination with lblod/app-gelinkt-notuleren#156

[nvdk]

looks good to me 👍

[lagartoverde]

Looks good to me

[abeforgit]

getting the same error as here:
#431 (review)

[elpoelma]

getting the same error as here: #431 (review)

Aha ok, should be fixed now. The issue was that when I reset the inverses to null for some models which had their inverse as null before, I forgot to check if the other side of the relationship also had inverse: null. That should be fixed now, I rechecked all inverses and don't see anymore issues with the meeting page.