[#43] App: Use FileSystemWatcher to renew contexts on demand

Elwig/Windows/AdministrationWindow.cs

@@ -103,7 +103,7 @@ namespace Elwig.Windows {
 
         abstract protected void UpdateButtons();
 
-        protected override async Task OnRenewContext() {
+        protected override async Task OnRenewContext(AppDbContext ctx) {
             for (int i = 0; i < PlzInputs.Length; i++)
                 await UpdatePlz(PlzInputs[i], PlzOrtInputs[i]);
         }