Add ability to log OBD data

[lamemakes]

It would be great if functionality existed to log the data displayed by the OBD functionality to file on the local system.

This is an option that should exist within the UI rather than the config.json, as a user should be able to very easily enable/disable it, create new logs, and even specify which OBD fields they want logged (see Add a new OBDII/ELM327 stat to query)

This would be a reasonably large feature, requiring sizable changes on both the UI & backend.