ZEPPELIN-50 Session History implementation.
Take care of SimpleDateFormat class thread safety.
Implement history selector GUI
Make history right after script finished.
Proper handling session selections
Report link take care of history
Make 'delete' button remove only a history, when page displaying history.
Refresh history list after new history made.
Make history view disables editor, run button, schedule button
Change 'session' -> 'job'
Change session -> job in unittest
make code more readable
Merge pull request #17 from NFLabs/session_history

ZEPPELIN-50 Session History implementation.