make the code that determines which axis to use explicit

In the previous changeset the code that determined
which axis the plots used was implemented as a
side effect of getting the Gnuplot definition of
an axis.
Changed that to an explit update call with simpler
logic.

pdb-plotting/src/main/java/org/lucares/recommind/logs/AxisSettings.java

@@ -10,7 +10,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 public class AxisSettings {
 
   public enum Type {
-    Number, Time, Duration
+    Number, Time, Duration, Percent
   }
 
   private String format = "";