Create a log of how PSCs are used

Create a log to see where the usage of PSCs is happening. Perhaps this could just be a dev thing to start or maybe it can be in the Gridsync log, for now.

In the future, we will want to have a nice, user friendly interface to display this information, but that discussion is out of scope for this ticket. We just need the practical logging for our own identification of bugs and understanding of PSC usage, for this one.