Print how many less circuits we'd need to build if Onionperf data would be used

In #44 (closed) we gave some rough estimations about the amount of circuits we'd need to build to cover the whole network. We could reduce that number further (and be faster) by taking Onionperf data into account.

There are two parts to this task involved:

1. Come up with a plan and implement it on how to make best use of the Onionperf instances we have (should we take all into account or only some/one e.g.?).
2. Update the information exposed in #44 (closed) accordingly.