clay: print download progress for desk updates

[yosoyubik]

WIP

(Note: possible alternative version of #6867; instead of scrying the rate out of %ames we rely on %ames notifying any subscribers for a %keen—In this case %clay, which will just send the %rate %gift to %kiln. Leaving as a draft so we can compare what approach is more ergonomic and also to consider a better UI for displaying the progress)

[yosoyubik]

This connects %hood to the console and, although not currently
used, adds the sole-id to %kiln, for possible later use in printing
more fine-grained information about desks' state. Another option
could be to have a separate console-enabled agent that manages
any information that needs to be printed, and then %kiln or the
related strandio threads can just poke it (this will possible end up
recreating the state stored in %kiln)

[yosoyubik]

Currently this only supports the view of how many paths are in flight.
The facilities for knowing the the size of any/all paths in the desk are
in place but are still a work in progress.

There is also a thread (-whit) that calculates the size of data at a path
based on the number of fragments and the size of each, as sent by the
publisher.

[yosoyubik]

demo of usage of global progress rate:

[yosoyubik]

Bandwidth demo:

[jalehman]

This is really great work! A thought that comes to mind:

Having this in the dojo as toggle-able behavior is desirable. It'll also be the case that many applications that eventually leverage fine for pulling content from other nodes will also want to be able to display download bandwidth/progress.

Providing documentation on how it works as a guide in the docs should accompany its release.