NAS / Remote file loading

[JoeMatt]

Work in Progress ticket

Specifically for tvOS which has limited storage and no UIDocumentPicker

Requirements:

• Expand PVFile to support lazy-loading of remote files
• Temporary caching of files locally (requires whole file on disk most likely)
• Should warn on large file copies, cancelable etc
• Maybe use FileProvider ... more to fill in.

Maybe see what VLC and other projects do

https://github.com/videolan/vlc-ios/tree/master/Apple-TV