Plain timeline styler (#94)

* #92 Create `TimelineStyle` and store it in user defaults

* #92 Create `TimelineStyler` observable environment object

* #92 Use timeline list row insets from the styler

* #92 remove sender view, move header into the styler views

* #92 Add timeline style option in settings

* #92 Add changelog

* #92 refactor some code duplications

* #92 Fix `TimelineStyle`targets

* #92 Fix `TimelineStyle` targets

* #92 Fix PR remarks

* #92 Fix inline PR comments

* #92 Fix UI tests

* #92 Rename bubbled to bubbles

ElementX/Sources/Other/ElementSettings.swift

@@ -0,0 +1,36 @@
+//
+//  ElementSettings.swift
+//  ElementX
+//
+//  Created by Ismail on 24.06.2022.
+//  Copyright © 2022 Element. All rights reserved.
+//
+
+import Foundation
+import SwiftUI
+
+/// Store Element specific app settings.
+final class ElementSettings: ObservableObject {
+
+    // MARK: - Constants
+
+    public enum UserDefaultsKeys: String {
+        case timelineStyle
+    }
+
+    static let shared = ElementSettings()
+
+    /// UserDefaults to be used on reads and writes.
+    static var store: UserDefaults {
+        .standard
+    }
+
+    private init() {
+        // no-op
+    }
+
+    // MARK: -
+
+    @AppStorage(UserDefaultsKeys.timelineStyle.rawValue, store: store)
+    var timelineStyle = BuildSettings.defaultRoomTimelineStyle
+}