Clean up code for BenchHub

[at15]

Major issues

• benchmark related code will be split into libstdb-go and xephon-b
• [collector] Moved to benchhub/lib/monitor #62 move collector somewhere else, might be benchhub, or gommon
• add tracing on server side to know where is our hot spot
• use go.ice as server framework

TODO

• group and clean up old issues, a new tag pre-benchhub should be added
• make the cassandra backend work again, it should be very easy without rich tag support
• recap the column store, it should support read at least
  • the inverted index can just be kept in memory and rebuilt when start, I don't think there is time to deal with high carnality
  • might take the time and port it to gegecece ...