[ZEPPELIN-451] Save codes and messages as multi-line

[sixmen]

What is this PR for?

Save Paragraph texts and result msgs as array of strings instead of one long string.
One long strings are not VCS-friendly.

What type of PR is it?

Improvement

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-451

How should this be tested?

Modify notebooks and check saved note files

Screenshots (if appropriate)

### Questions: - Does the licenses files need update? NO - Is there breaking changes for older versions? Notebooks from new zeppelin can not be imported in old zeppelin. - Does this needs documentation? NO

[anthonycorbacho]

@sixmen thank you for your contribution, this feature looks AWESOME.
I didnt dive into the code, but one question came in my mind;

This change is kinda breaking change since the notebook format is now different from what we have. So what can be the best way in your opinion to support old notebook format?

[sixmen]

It supports old notebook format.
Old code can not read new notebook format, but it can not be helped any way.
So I think it is an endurable breaking change.

[sixmen]

I worked again for this commit with recent sources.
I hope someone reviews this pull request.
As I know, there are already breaking changes in the notebook format. So it does not matter with this PR.