refactor and cleanup [skip ci]

submodules/Postbox/Sources/AdditionalChatListItemsView.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+final class MutableAdditionalChatListItemsView: MutablePostboxView {
+    fileprivate var items: Set<PeerId>
+    
+    init(postbox: Postbox) {
+        self.items = Set(postbox.additionalChatListItemsTable.get())
+    }
+    
+    func replay(postbox: Postbox, transaction: PostboxTransaction) -> Bool {
+        if let items = transaction.replacedAdditionalChatListItems {
+            self.items = Set(items)
+            return true
+        }
+        return false
+    }
+    
+    func immutableView() -> PostboxView {
+        return AdditionalChatListItemsView(self)
+    }
+}
+
+public final class AdditionalChatListItemsView: PostboxView {
+    public let items: Set<PeerId>
+    
+    init(_ view: MutableAdditionalChatListItemsView) {
+        self.items = view.items
+    }
+}