Incremental diff implementation

[genadyp]

For more details about incremental diff #270

TODO

• ContentDataDb should be taken into action with a ContentServer
• Use a ContentDataDb#get to initialize the system instead of ContentData object stored at Params['local_content_data_path']
• End-to-end testing
• (Optional - need to ask Shiray) Add to file_utils a functionality to
  • diff between two timestamps
  • snapshot for the date
• performance tests for ContentDataDb

[bbfsdev]

So basically this can already be used, right?
Did you do a pull request? (did you pushed your local branch?)

[genadyp]

Pull Request

@yarondbb
@kolmanv
Review please

---

Basically we can use it after the code review and resolving the three first task from the TODO list

[genadyp]

Branch merged