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/Services/AppSettingsService.cs

@@ -0,0 +1,41 @@
+using System;
+using Bit.App.Abstractions;
+using Plugin.Settings.Abstractions;
+
+namespace Bit.App.Services
+{
+    public class AppSettingsService : IAppSettingsService
+    {
+        private readonly ISettings _settings;
+
+        public AppSettingsService(
+            ISettings settings)
+        {
+            _settings = settings;
+        }
+
+        public bool Locked
+        {
+            get
+            {
+                return _settings.GetValueOrDefault(Constants.Locked, false);
+            }
+            set
+            {
+                _settings.AddOrUpdateValue(Constants.Locked, value);
+            }
+        }
+
+        public DateTime LastActivity
+        {
+            get
+            {
+                return _settings.GetValueOrDefault(Constants.LastActivityDate, DateTime.MinValue);
+            }
+            set
+            {
+                _settings.AddOrUpdateValue(Constants.LastActivityDate, value);
+            }
+        }
+    }
+}