zjffdu [ZEPPELIN-3758]. Convert old note file note.json to new style
### What is this PR for?
This PR is follow up of ZEPPELIN-261, it is to convert old note file note.json to new style when user upgrading zeppelin before 0.9. 2 properties are introduced.
* `zeppelin.notebook.new_format.convert`, by default it is false. When enabled, zeppelin will first find all the old note file note.json and then convert it into new style.
* `zeppelin.notebook.new_format.delete_old`, by default it is false, when setting true, zeppelin will delete the old note file after converting it into new style.

### What type of PR is it?
[Improvement]

### Todos
* [ ] - Task

### What is the Jira issue?
* https://issues.apache.org/jira/browse/ZEPPELIN-3758

### How should this be tested?
* CI pass

### Screenshots (if appropriate)

### Questions:
* Does the licenses files need update? No
* Is there breaking changes for older versions? No
* Does this needs documentation? No

Author: Jeff Zhang <zjffdu@apache.org>

Closes #3189 from zjffdu/ZEPPELIN-3758 and squashes the following commits:

5b59dcc [Jeff Zhang] [ZEPPELIN-3758]. Convert old note file note.json to new style
Latest commit fa271b9 Sep 25, 2018