Add Simple Template Example

- Add a simple Template example that shows a user profile with avatar, displayName and presence.
- ScreenCoordinator: closure based with less protocols and delegates.
- Reducer: Reducer function that manages all state modifications.
- SwiftUI View: Decomposes UI into appropriate sub components.
- Uses Theme and Dependency Management Infrastructure

Riot/Modules/Common/SwiftUI/VectorHostingController.swift

@@ -27,12 +27,21 @@ class VectorHostingController: UIHostingController<AnyView> {
     // MARK: Private
     
     private var theme: Theme
+
+    init() {
+        self.theme = ThemeService.shared().theme
+        super.init(rootView: AnyView(EmptyView()))
+    }
     
     init<Content>(rootView: Content) where Content: View {
         self.theme = ThemeService.shared().theme
         super.init(rootView: AnyView(rootView.vectorContent()))
     }
     
+    func setRoot<V: View>(view: V) {
+        rootView = AnyView(view)
+    }
+    
     required init?(coder aDecoder: NSCoder) {
         fatalError("VectorHostingViewController does not currently support init from nibs")
     }