PauseButton: eliminate potential race condition
New LED behaviour: off = not paused, not running. flash = paused. on = executing blocks. Implemented with new PlayLed module
Pauser: add method bool paused()
PlayLed: light off at boot
PlayLed: use Pauser::paused() instead of referencing PauseButton.

PauseButton: no longer need static self-reference
USBSerial: remove special handling of \r
Merge remote-tracking branch 'upstream/edge' into feature/add-est-to-progress
Don't display ETA for first 10 seconds
don't accumulate time if paused