Report storage status in configtest

This is a prototype implementation for issue #71 - still completely
lacking the part of being optional.

ATxConfigTest/AutoTxConfigTest.cs

 using System;
 using System.IO;
+using ATxCommon;
 using ATxCommon.Serializables;
 using NLog;
 using NLog.Config;
@@ -48,6 +49,9 @@ namespace ATxConfigTest
                 Console.WriteLine($"\n{mark} configuration settings {mark}");
                 Console.Write(_config.Summary());
                 Console.WriteLine($"{mark} configuration settings {mark}\n");
+                var storage = new StorageStatus(_config);
+                Console.Write(storage.SpaceSummary());
+                Console.Write(storage.GraceLocationSummary());
             }
             catch (Exception ex) {
                 Console.WriteLine(ex);