Implement Webservice interface for fetching the fact candidate of a Wikidata entity

[anbo-de]

As a developer, I want to see existing facts.

• [x] As a dev, I want to see fact candidates from the new service retrieved via RESTful call for a specific Wikidata entity (e.g., GET /facts/Q1106)

[lalit97]

PR: https://github.com/WikidataComplete/wikidatacomplete-backend/pull/14

1. Current API
   

2. New API

[Perevalov]

@anbo-de We checked it, looks good. Please, review and close the issue if everything is ok

[lalit97]

closed with #14 and #20