Improve Theming (#1707)

* Improved theming logic and performance, also fixed some issues regarding changing the theme after vault timeout and fixed theme applying on password generator/history

* Removed messenger from theme update, and now the navigation stack is traversed and each IThemeDirtablePage gets theme updated

* Improved code on update theme on pages

src/App/Pages/Generator/GeneratorPage.xaml.cs

@@ -1,15 +1,15 @@
-using Bit.App.Resources;
-using System;
+using System;
 using System.Threading.Tasks;
+using Bit.App.Resources;
+using Bit.App.Styles;
 using Bit.Core.Abstractions;
 using Bit.Core.Utilities;
 using Xamarin.Forms;
-using Xamarin.Forms.PlatformConfiguration;
 using Xamarin.Forms.PlatformConfiguration.iOSSpecific;
 
 namespace Bit.App.Pages
 {
-    public partial class GeneratorPage : BaseContentPage
+    public partial class GeneratorPage : BaseContentPage, IThemeDirtablePage
     {
         private readonly IBroadcasterService _broadcasterService;
         
@@ -49,7 +49,7 @@ namespace Bit.App.Pages
             }
             if (isIos)
             {
-                _typePicker.On<iOS>().SetUpdateMode(UpdateMode.WhenFinished);
+                _typePicker.On<Xamarin.Forms.PlatformConfiguration.iOS>().SetUpdateMode(UpdateMode.WhenFinished);
             }
         }
 
@@ -61,18 +61,19 @@ namespace Bit.App.Pages
         protected async override void OnAppearing()
         {
             base.OnAppearing();
+
+            lblPassword.IsVisible = true;
+
             if (!_fromTabPage)
             {
                 await InitAsync();
             }
-            _broadcasterService.Subscribe(nameof(GeneratorPage), async (message) =>
+
+            _broadcasterService.Subscribe(nameof(GeneratorPage), (message) =>
             {
                 if (message.Command == "updatedTheme")
                 {
-                    Device.BeginInvokeOnMainThread(() =>
-                    {
-                        _vm.RedrawPassword();
-                    });
+                    Device.BeginInvokeOnMainThread(() => _vm.RedrawPassword());
                 }
             });
         }
@@ -80,6 +81,9 @@ namespace Bit.App.Pages
         protected override void OnDisappearing()
         {
             base.OnDisappearing();
+
+            lblPassword.IsVisible = false;
+
             _broadcasterService.Unsubscribe(nameof(GeneratorPage));
         }
 
@@ -141,5 +145,12 @@ namespace Bit.App.Pages
                 await Navigation.PopModalAsync();
             }
         }
+
+        public override async Task UpdateOnThemeChanged()
+        {
+            await base.UpdateOnThemeChanged();
+
+            await Device.InvokeOnMainThreadAsync(() => _vm?.RedrawPassword());
+        }
     }
 }