Remove Web UI components and their deps from tree

Web UI and dependencies added by it are beyond the updated scope
of Rubick project (see README file for updates of scope).
This change removes components of Web UI (front-end related code)
and components of API service (celery, flask etc).
Update README to reflect the current scope of Rubick project.

blueprint decouple-ui

Change-Id: I302626395c1a677871ac5154f2064bef400be3f1