Improve casting interface for Entities

[MichaelHirn]

Especially Individuals and standardize a bit better so that implementing higher-level entity factories becomes easier and requires less overhead.

[MichaelHirn]

Just one example

• .find requires extra casting into correct higher-level entity factory

const entity = await rlayClient.HighLevelCustomEntity.find(cid)
// right now: entity.constructor.name === 'Rlay_Individual'
// should be: entity.constructor.name === 'HighLevelCustomEntity'
// to get it to `HighLevelCustomEntity` you have to do rn:
const castedEntity = new rlayClient.HighLevelCustomEntity(rlayClient, entity.payload);
castedEntity.remoteCid = entity.remoteCid;