JSON storage, robot synchronization, and shutdown

Operation	CobottaCtrl	Other devices
Startup	Read robot P variables	Load JSON
Current position	DeviceProxy	DeviceProxy
Teaching	Write robot and read back	Update JSON
Clear	Write robot and read back	Update JSON
Remove from list	Keep robot value	Also remove from JSON
Explicit JSON save	Save to selected file	Save to selected file

JSON format

{
  "P0": [
    0,
    0,
    0,
    0,
    0,
    0,
    -1
  ],
  "P1": [
    100,
    200,
    300,
    0,
    0,
    0,
    -1
  ]
}

This is a format example, not a guarantee about the coordinate format used by every robot. The Model loads keys consisting of P followed by digits. The JSON root must be an object.

Saving on exit synchronizes changed displayed values to Cobotta, then writes the default JSON file. Rows removed from the display are not deleted from the robot. A communication or file error may leave partial changes; back up important coordinates before overwriting them.