Save error is now handled via Messenger instead of unhandled exception handler (which didn't work)

Save as actually works now
WIP Styles
Code cleanup

ModernKeePass/ViewModels/MainVm.cs

@@ -183,6 +183,7 @@ namespace ModernKeePass.ViewModels
                         }
                         catch (SaveException exception)
                         {
+                            // TODO: Implement save as
                             _notification.Show(exception.Source, exception.Message);
                             return;
                         }