switch to using `ledger` for device settings

[sebkopf]

this eliminates issues of discontinuity between the settings of a device and with the 16KB limit it can easily store all settings:

https://docs.particle.io/getting-started/logic-ledger/ledger-configuration/

notes:

• keep the settings changes happening on the device side with the commands (faster than sync)
• i.e. beyond using this for easy sync instead of eeprom, consider keeping everything as is (except use the ledger to figure out status of everything on lablogger app since this way don't need to query the device)

[sebkopf]

don't think that's necessary after all with the SDDS implementation