Lock Screen Fixes

- Move settings to AppSettingsService
- Update activity on page disappaearing
- Always check if app is currently locked before updating last activity
date

src/App/Abstractions/Services/IAppSettingsService.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace Bit.App.Abstractions
+{
+    public interface IAppSettingsService
+    {
+        bool Locked { get; set; }
+        DateTime LastActivity { get; set; }
+    }
+}