ideal Version
Retrieves the ideal version.
It is the version that the device will reach if all downloadable firmwares are downloaded and if all applicable updates are applied. This version is not necessarily local.
Note: this version might differ from the greater version of all downloadable and applicable firmwares if, and only if, the ideal firmware is local but cannot be applied because an intermediate, not downloaded firmware is required first.
Return
the ideal version, or null
if the device is up to date