Measurement container performance scales poorly

[leokoppel]

An informal report from @navganti

Platform

xenial 64

Steps to Reproduce

1. Add items to landmark measurement containers

Observed result

Operations become noticeably slow unless old items are deleted from the container.

Should add a benchmark first to determine which operations are slow, then determine how to fix.

[leokoppel]

The benchmarks in #228 reveal MeasurementContainer::get() is terribly inefficient: O(NlogN) instead of expected O(logN).