Add notebook REST API for create, delete and clone operations

Based on community request the goal of this issue is to add REST API for notebook create, delete and clone operations.
This will be done by adding the appropriate functions to the existing NotebookRestApi class.

NotebookRestAPI class already has access to Notebook zengine class in the constructor
public NotebookRestApi(Notebook notebook)

So implementation is just involving exposing the following methods:
createNote
removeNote

cloneNote is implemented in the NotebookServer class and not in the notebook zengine class. to make sure implementation is the same for socket API and REST API, we will refactor zengine notebook class to implement the clone operation and call on this method by both REST and Socket API.

Any comments are welcome.