mesh.calibrate(seconds) utility

In the quest to make a simple mesh calibration utility, multiple new facilities were required and some odds and ends were fixed.

This adds the commands:

* `mesh.calibrate(seconds)` - run a mesh calibration ping once a second for this many seconds, the scout running the calibrate will blink red for no mesh, yellow for weak mesh, and green for mesh, and every other scout it is meshed with will blink blue
* `mesh.from` - returns the scout id that last commanded this scout (useful to auto-generate replies)
* `mesh.each("command")` - will run `command(id,lqi,via)` for every other scout currently visible on the mesh (as seen with `mesh.routing`)

It also enables multiple commands to be sent simultaneously.