Expand "create notebook" of REST API to have initial paragraphs

Issue starts from here.

http://mail-archives.apache.org/mod_mbox/incubator-zeppelin-dev/201512.mbox/%3CCAF5108ikq69-bMXuocHB50cUucNrWJbiuY0n%3DrkN2pFdi5i86Q%40mail.gmail.com%3E

Current REST API doesn't have the feature - updating content of the paragraph.

We may have to check UI issue (or side-effect, if any) when implementing CRUD to paragraph via REST API.

Before going further, there's a way to minimize potential side-effect, providing initial paragraphs when creating new notebook via REST API.
Users couldn't see new notebook before persisted so I believe it doesn't make any noise with UI interaction.