Add a "load more" button instead of always inserting events in timelines

Changelog-Added: Add a "load more" button instead of always inserting events in timelines

damus/Views/Timeline/LoadMoreButton.swift

@@ -0,0 +1,50 @@
+//
+//  LoadMoreButton.swift
+//  damus
+//
+//  Created by William Casarin on 2023-02-20.
+//
+
+import SwiftUI
+
+struct LoadMoreButton: View {
+    @ObservedObject var events: EventHolder
+    let scroller: ScrollViewProxy?
+    
+    func click() {
+        events.flush()
+        guard let ev = events.events.first, let scroller else {
+            return
+        }
+        scroll_to_event(scroller: scroller, id: ev.id, delay: 0.1, animate: true)
+    }
+    
+    var body: some View {
+        Group {
+            if events.queued > 0 {
+                Button(action: click) {
+                    Text("Load \(events.queued) more")
+                }
+                .font(.system(size: 14, weight: .bold))
+                .padding(10)
+                .frame(height: 30)
+                .foregroundColor(.white)
+                .background(LINEAR_GRADIENT)
+                .clipShape(Capsule())
+            } else {
+                EmptyView()
+            }
+        }
+    }
+}
+
+struct LoadMoreButton_Previews: PreviewProvider {
+    @StateObject static var events: EventHolder = test_event_holder
+    
+    static var previews: some View {
+        LoadMoreButton(events: events, scroller: nil)
+    }
+}
+
+
+let test_event_holder = EventHolder(events: [], incoming: [test_event])