ZEPPELIN-50 Session History implementation.

Session History implementation. I wrote api implementation, there's no GUI implementation yet. here's implementation detail.

* current session persistent file path is changed from ZEPPELIN_SESSION_DIR/sessionId to ZEPPELIN_SESSION_DIR/sessionId/current
* each history is saved at ZEPPELIN_SESSION_DIR/sessionId/history/yyyy-MM-dd_HHmmss_SSS
* History is automatically created only if session (run and) finished successfully.

Next step is implement GUI