Duplicate Checks for composites

[pajoma]

Repeated push of new entities will create duplicates for nested objects, example:

[<https://graph.dev-e365.ext-env.av360.org/api/s/vhs-lernportal/entities/v_t5epxx>](https://graph.dev-e365.ext-env.av360.org/nav/node?id=%2Fapi%2Fs%2Fvhs-lernportal%2Fentities%2Fv_t5epxx&)
    [schema:offers](http://schema.org/offers) [<https://graph.dev-e365.ext-env.av360.org/api/s/vhs-lernportal/entities/bz722bp0>](https://graph.dev-e365.ext-env.av360.org/nav/node?id=%2Fapi%2Fs%2Fvhs-lernportal%2Fentities%2Fbz722bp0&)

[<https://graph.dev-e365.ext-env.av360.org/api/s/vhs-lernportal/entities/o72w1x3a>](https://graph.dev-e365.ext-env.av360.org/nav/node?id=%2Fapi%2Fs%2Fvhs-lernportal%2Fentities%2Fo72w1x3a&) 
  a [schema:Offer;](http://schema.org/Offer) 
  [schema:price](http://schema.org/price) 5.26E1; 
  [schema:priceCurrency](http://schema.org/priceCurrency) "EUR"@de . 
[<https://graph.dev-e365.ext-env.av360.org/api/s/vhs-lernportal/entities/msmfpv2a>](https://graph.dev-e365.ext-env.av360.org/nav/node?id=%2Fapi%2Fs%2Fvhs-lernportal%2Fentities%2Fmsmfpv2a&) 
  a [schema:Offer;](http://schema.org/Offer) 
  [schema:price](http://schema.org/price) 5.26E1; 
  [schema:priceCurrency](http://schema.org/priceCurrency) "EUR"@de .

Issue here: random generated identifiers for composites

Proposed solutions:

• nested objects should be Bnodes. When creating the id, we should use immutable properties (type, ..) for the seed, to have it reproducible