Channels performance improvements

Add settings:
Show channel avatars in channels lists
Show channel avatars in videos lists

Fix #508

Shared/Channels/ChannelAvatarView.swift

@@ -9,11 +9,13 @@ struct ChannelAvatarView: View {
     @ObservedObject private var accounts = AccountsModel.shared
     @ObservedObject private var subscribedChannels = SubscribedChannelsModel.shared
 
+    @State private var url: URL?
+
     var body: some View {
         ZStack(alignment: .bottomTrailing) {
             Group {
                 Group {
-                    if let url = channel?.thumbnailURLOrCached {
+                    if let url {
                         ThumbnailView(url: url)
                     } else {
                         ZStack {
@@ -31,6 +33,7 @@ struct ChannelAvatarView: View {
                             .font(.system(size: 20))
                             .contentShape(Rectangle())
                         }
+                        .onAppear(perform: updateURL)
                     }
                 }
                 .clipShape(Circle())
@@ -54,6 +57,16 @@ struct ChannelAvatarView: View {
         }
         .imageScale(.small)
     }
+
+    func updateURL() {
+        DispatchQueue.global(qos: .userInitiated).async {
+            if let url = channel?.thumbnailURLOrCached {
+                DispatchQueue.main.async {
+                    self.url = url
+                }
+            }
+        }
+    }
 }
 
 struct ChannelAvatarView_Previews: PreviewProvider {