Pass data and context to queryHelpers

[smelukov]

addQueryHelpers({
  foo() {
    console.log(this.data);
    console.log(this.context);
  }
})

[lahmatiy]

Starting Discovery.js 1.0.0-beta.80 (jora 1.0.0-beta.10) custom methods are support for accessing to context via this.context. Custom methods can be a string (jora query) as well, and access to context via # as a regular queries.

Accessing to root data in methods via this.data is not supported. This limitation is due a custom method can be a string (jora query) and @ (or this.data) refers to query root or the method itself instead of root query.