Export WoT implementation type

[relu91]

Currently, when you are using the core package you are bound to the Scripting API interface. This limits us in experimenting with new features before "standardization" we need an extension mechanism to help developers use node-wot-only features. One starting point could be to expose the internal types (e.g., WoT Implementation) to have typescript-checked extensions. Taking for example the new work item on making schema validation optional, with the current settings is not possible for a user to ever use a new parameter for disabling the validation per affordance.