Issue #61: Add route to return sources

specs/blendb-api-v1.raml

src/api/controllers/engine.spec.ts

src/api/controllers/engine.ts

src/api/middlewares/engine.ts

src/api/router-v1.ts

src/api/types.ts

src/common/query.ts

src/core/engine.ts

src/core/server.spec.ts

src/core/server.ts

src/core/source.ts

src/core/transformer.spec.ts

src/core/view.ts

src/util/configParser.ts

src/util/graph.ts