Decouple run summary properties from specific file types

This lets us display runs on the home page and results detail page
properly when there is only a results.zip file and no standalone
results.json file.

Fixes #11

This also moves us closer to a fix for #12, since the properties that are
relative to the current wall clock time are no longer being cached.

src/main/java/tfb/status/handler/UploadResultsHandler.java

@@ -187,13 +187,13 @@ private Path destinationForIncomingFile(Path incomingFile)
       if (results == null)
         return newResultsFile();
 
-      if (results.json != null
-          && results.json.fileName.endsWith("." + fileExtension))
-        return fileStore.resultsDirectory().resolve(results.json.fileName);
+      if (results.jsonFileName != null
+          && results.jsonFileName.endsWith("." + fileExtension))
+        return fileStore.resultsDirectory().resolve(results.jsonFileName);
 
-      if (results.zip != null
-          && results.zip.fileName.endsWith("." + fileExtension))
-        return fileStore.resultsDirectory().resolve(results.zip.fileName);
+      if (results.zipFileName != null
+          && results.zipFileName.endsWith("." + fileExtension))
+        return fileStore.resultsDirectory().resolve(results.zipFileName);
 
       return newResultsFile();
     }