Fix all bench_tests
Get insertion benchmark running

On my machine I can insert at ~130k rows/s, flushing every 50k rows,
onto a spinning disk. Should be plenty fast for now.
Hit slice grouping in the bench tests for apples-to-apples comparison
Fix a TODO
Less redundant HandlerFunc naming
Return dimension table row names as a plain array

Including the index is duplicate information the callers end up stripping out.
Add route to get a single dimension
Port a partial change over from master.

Taken from 443dfd2d0d5e6a61a1ead5e39effd33b1f4a1c5e.