125 revisit schema implementation

[kukeiko]

revisited schema implementation:

• no longer using the JSON format of a schema as ctor argument; was not intuitive enough (and too coupled)
• allOf/anyOf/oneOf not working yet
• properties not fully working yet
• relations, indexes & keys are working to the extent of having current workspace playground specs run through
• some other stuff

should now be a good basis to continue working on end to end scenarios. at least I hope so, because I am a bit sick of redoing schema implementations.