Expand 'Last Download' Dates to cater for things like Device Unload

1. Download a device.
2. Last download date is set to present date and time.
3. Unload the device.
4. The last download date is still set to the previous date and time, despite the fact that the device 'is not downloaded'.

Things like this need to be catered for in the ETS software. ETS should (by default) record and make available to the user a proper chronology of the interactions with devices.