Check and log a warning on `data-streamed` with `download` attribute

[dascritch]

Even if we indicate in the documentation https://github.com/dascritch/cpu-audio/blob/master/INSTALL.md#indicate-a-prefered-downloadable-audio-resource to not use download attributes indicators when a media is indicated as streamed, I think it may be useful to indicate in a warn() this kind of misconfiguration.

IMHO, the best way to do it is to do an integrity check at CpuAudioElement class instantiation during the copyAttributesToMediaDataset() step.