Bugfix/large playlist crash (#111)

* get all song coverArt as they are rendered

doing it all up front was too heavy
temporarily disabled mapping artwork in setQueue, need to fix this

* use cache data for track artwork when available

* fix round art in context menu for songs

* set only the first artwork at play time

then set the rest in the playback service

* handle both cached images and fetching images

* remove commented code

* fix shuffle

fix first thumbnail not being updated on shuffle for now playing background

app/models/library.ts

@@ -43,7 +43,6 @@ export interface Song {
   discNumber?: number
   duration?: number
   starred?: number
-  coverArt?: string
   playCount?: number
   userRating?: number
   averageRating?: number