Add Cover art support

[jherby2k]

Album cover art metadata should be supported. That includes loading/unloading from external files, as well as encoder and decoder support.

[bherila]

+1 😄

BTW, I'm planning to organize some of my spaghetti code GUI for fixing up mp3 libraries and make it a more generic and well written tool built on top of PowerShellAudio. The code I have is currently here: https://bitbucket.org/bherila/mp3fix and I'm planning to move it to Github soon! So thank you for helping me to revive this side project 👍