Consolidate images and files

CHDataManagement/Main/SelectedContentView.swift

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+import SwiftUI
+
+struct SelectedContentView<Contained>: View where Contained: MainContentView {
+
+    @Binding
+    var selected: Contained.Item?
+
+    init(selected: Binding<Contained.Item?>) {
+        self._selected = selected
+    }
+
+    var body: some View {
+        if let item = selected {
+            Contained(item: item)
+        } else {
+            HStack {
+                Spacer()
+                Text("Select \(Contained.itemDescription) from the sidebar")
+                    .font(.largeTitle)
+                    .foregroundColor(.secondary)
+                Spacer()
+            }
+        }
+    }
+}