New toast action to show toast messages from XAML

Code cleanup for Sonar
Tests corrections

ModernKeePass/Exceptions/NavigationException.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace ModernKeePass.Exceptions
+{
+    public class NavigationException: Exception
+    {
+        public NavigationException(Type pageType) : base($"Failed to load Page {pageType.FullName}")
+        {
+        }
+    }
+}