fix missing/wrong logging

1. Log the exception in PdbFileIterator with a logger instead
   of just printing it to stderr.
2. Increase log level for exceptions when inserting entries.
3. Log exception when creation of entry failed in TcpIngestor.

pdb-ui/src/main/java/org/lucares/pdbui/TcpIngestor.java

@@ -124,6 +124,7 @@ public class TcpIngestor implements Ingestor, AutoCloseable, DisposableBean {
 				final Entry entry = new Entry(date, duration, tags);
 				return Optional.of(entry);
 			} catch (final Exception e) {
+				LOGGER.error("Failed to create entry.", e);
 				return Optional.empty();
 			}
 		}