[NB] Emit electrode[-pair] selected signals
[NB] Emit electrode[-pair] selected signals

Emit `electrode-selected` and `electrode-pair-selected` signals from
`DmfDeviceCanvas`.

Maintain electrode states and routes as attributes of the
`DmfDeviceCanvas`.

Render colors of electrodes based on electrode states and render routes
as lines with a square/rectangle marker indicating the route end-point.

wheeler-microfluidics/dmf-device-ui