Added line in DBAccess to remove the ThreadLocal after we're done with it; added Comparator to Sample so that we can add null parents; wrote POST test for SampleResource with null and not-null parent check; re-did the spacing in SampleIDResourceTest

Former-commit-id: d421cec

Author: morgantaschuk

seqware-common/src/main/java/net/sourceforge/seqware/common/factory/DBAccess.java

@@ -105,6 +105,7 @@ public synchronized static void close() {
             metadataDBWrapper.set(null);
             //db = null;
         }
+        metadataDBWrapper.remove();
     }
 
     private DBAccess() {