Add a skip silence feature to calls.

During calls there are often moments of "dead air". A feature to optionally skip this segments would make listening to calls faster, and hopefully, smoother.

The issue names no files, tests, or entry points. First locate the call playback path and determine how silence can be detected and skipped; done means an optional setting skips dead-air segments during calls without disrupting the audible conversation.

Written by the indexing model from the issue text.