Parsing, Default Manipulation and Validation Discussion

In #3 there were discussions on what to do to align "parsing", validation and default manipulation between playground and node-wot. I think there should be one codebase that does all that among Node.js based Thingweb components and we have some work to do towards that. Below are the important remarks from #3:

- node-wot td parser, in consuming step, corrects user inputs (if readonly is not boolean, it is corrected to boolean) and fills defaults. This can be done by the core package as this is not needed as an external tool
- We should align the default addition mechanism to use ajv and share the library between playground web and node-wot. A JSON Schema can contain default values already. Anything that needs conditions (if readOnly: false, op has writeproperty) can be programmed on top.
- [td-parser.ts](https://github.com/eclipse-thingweb/node-wot/blob/master/packages/td-tools/src/td-parser.ts): maybe rename it since it is a serializer as well or split the functionality
- [resolver-interface.ts](https://github.com/eclipse-thingweb/node-wot/blob/master/packages/td-tools/src/resolver-interface.ts): not sure whether we actually need this interface used by helpers and thing-model
- [td-helpers.ts](https://github.com/eclipse-thingweb/node-wot/blob/master/packages/td-tools/src/td-helpers.ts): has little functionality, maybe can be moved into node-wot/core
- Dependencies mentioned in comments there are now resolved