Decouple feathr rest and feathr core code.

• Feathr rest api code is not needed to be included in feathr package, feathr rest api is aimed to be deployed as a container app, not designed for being consumed as a library.
• Have two root namespaces in feathr is causing confusion to contributors. Furthermore, there is cyclic dependency between feathr rest api and feathr core.

Suggest doing this after feathr search and registry provider mvp work is completed to avoid merge