New Fature: Burst Detection (WIP)

This pull-request is server side of https://github.com/jubatus/jubatus_core/pull/43.
Please merge this pull request after https://github.com/jubatus/jubatus_core/pull/43 is merged.

**This pull-request is WIP; DO NOT MERGE yet.**

What is unimplemented:
- [ ] get_status
- [ ] distribution mode