add initial widevine drm support for audio url sources

See merge request !16

Fix channel content not showing older non-videos, fix seperated channel contents not being fetched if not both streams and videos are included

PeekChannelContent and initial algorithm support, DevSubmit support, Prevent crash url search before init, Documentation url scanning for devportal, limit ongoing downloads ui to 4

Deleting playlist video deletes local files, Post links are now clickable, going back to channel page from post now shows channel page correctly, search capabilities correct for channel content search, Fix loader not disappearing in certain cases on post details

Grayjay logo, WatchLater button, WatchLater download, Download notification dismiss fix, Polycentric open platform, Minor utility additions, Dev method documentation url support