* Refactor propagation delay estimator.
NOTE: It is not possible to calculate OWD (one-way-delay) in a passive
fashion. So, this should not be used for anything requiring high
precision.
But, mainly factoring it out as a separate object just in case it can be
re-used.
TODO:
- probably has some edge case that is not handled well
- maybe path change detection can be improved
- will write UT later. This is just purely splitting it out from what
was embedded in RTPStatsReceiver.
* fix labels
* precision -> accuracy