Layout change in CompositeKey user control

Button text is now settable
Opening database is placed in async task dispatcher to return control to the UI

ModernKeePass/Extensions/DispatcherTaskExtensions.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Threading.Tasks;
+using Windows.UI.Core;
+
+namespace ModernKeePass.Extensions
+{
+    public static class DispatcherTaskExtensions
+    {
+        public static async Task<T> RunTaskAsync<T>(this CoreDispatcher dispatcher,
+            Func<Task<T>> func, CoreDispatcherPriority priority = CoreDispatcherPriority.Normal)
+        {
+            var taskCompletionSource = new TaskCompletionSource<T>();
+            await dispatcher.RunAsync(priority, async () =>
+            {
+                try
+                {
+                    taskCompletionSource.SetResult(await func());
+                }
+                catch (Exception ex)
+                {
+                    taskCompletionSource.SetException(ex);
+                }
+            });
+            return await taskCompletionSource.Task;
+        }
+
+        // There is no TaskCompletionSource<void> so we use a bool that we throw away.
+        public static async Task RunTaskAsync(this CoreDispatcher dispatcher,
+            Func<Task> func, CoreDispatcherPriority priority = CoreDispatcherPriority.Normal) =>
+            await RunTaskAsync(dispatcher, async () => { await func(); return false; }, priority);
+    }
+}