[HER-1546] Springify(5): Update checkpointing to work smoothly with spring-configured crawls

stats & logging checkpoint support
* StatisticsTracker.java
    implement Checkpointable; save small state in JSON, recycle BDB data when recovering
* CrawlerLoggerModule.java
    implement Checkpointable; rotate logs on checkpoint
* GenerationFileHandler.java
    avoid clobbering leftover logs from earlier futures via moveAside
* CrawlStatSnapshot.java
    (sameProgressAs) test for lack-of-progress
* ObjectIdentityMemCache.java, TopNSet.java
    offer deeper access to assist checkpoint/resume

commons/src/main/java/org/archive/io/GenerationFileHandler.java

@@ -100,6 +100,7 @@ public class GenerationFileHandler extends FileHandler {
              storeSuffix;
         File activeFile = new File(filename);
         File storeFile = new File(storeFilename);
+        FileUtils.moveAsideIfExists(storeFile);
         if (!activeFile.renameTo(storeFile)) {
             throw new IOException("Unable to move " + filename + " to " +
                 storeFilename);