Channels layout improvements, other UI fixes

Shared/Modifiers/UnsubscribeAlertModifier.swift

@@ -0,0 +1,29 @@
+import Foundation
+import SwiftUI
+
+struct UnsubscribeAlertModifier: ViewModifier {
+    @EnvironmentObject<NavigationState> private var navigationState
+    @EnvironmentObject<Subscriptions> private var subscriptions
+
+    func body(content: Content) -> some View {
+        content
+            .alert(unsubscribeAlertTitle, isPresented: $navigationState.presentingUnsubscribeAlert) {
+                if let channel = navigationState.channelToUnsubscribe {
+                    Button("Unsubscribe", role: .destructive) {
+                        subscriptions.unsubscribe(channel.id) {
+                            navigationState.openChannel(channel)
+                            navigationState.sidebarSectionChanged.toggle()
+                        }
+                    }
+                }
+            }
+    }
+
+    var unsubscribeAlertTitle: String {
+        if let channel = navigationState.channelToUnsubscribe {
+            return "Unsubscribe from \(channel.name)"
+        }
+
+        return "Unknown channel"
+    }
+}