Added benchmarkjs as dev dependency. Updated benchmark tests

* Added delete to benchmark tests
* Keeping track of ids upon creation benchmark to pass to deletion
  benchmark. Looking the ids up out of an array might slightly affect
  the outcome of the benchmark, but it can't be helped.
* Indexes are not being deleted, also all posts/boards/threads are not
  all deleted because we arent specifying an exact sample size for each
  benchmark test