Add a placeholder for showing VI version on status page of Enabler.

See #148.
Remove unnecessary layout wrappers in diagnostic request view.
Merge remote-tracking branch 'origin/display-vi-version' into 167-vi-connected-callback
Disable existing VI when switching to trace data source.
Add a callback for when the VI connection status changes.

This also adds placholders for each VI to return the version.
Add a draft implementation of reading VI version for a USB VI.
Handle getting VI version (and waiting for request) in VehicleManager.
Add additional logging for VI callbacks.
Move handling of VI connection callbacks to VehicleService.
Ineffective changes to get VI callback working...
Allow disabling all VIs from Enabler settings menu.

Fixed #169.
Perform VI version query in thread separate from callback.

Fixed #168.
Merge pull request #168 from openxc/167-vi-connected-callback

Add a callback for VI connection and display version on status page