add logarithmic scaling for the y-axis

Often we have a few very high values and a lot
low values. With a linearly scaled y-axis the
plot is mostly useless.

pdb-ui/src/main/java/org/lucares/pdbui/domain/PlotRequest.java

@@ -13,6 +13,8 @@ public class PlotRequest {
 
 	private LimitBy limitBy = LimitBy.NO_LIMIT;
 
+	private YAxis yAxis = YAxis.LINEAR;
+
 	private int limit = Integer.MAX_VALUE;
 
 	private String dateFrom;
@@ -91,4 +93,11 @@ public class PlotRequest {
 		this.dateRange = dateRange;
 	}
 
+	public YAxis getAxisScale() {
+		return yAxis;
+	}
+
+	public void setAxisScale(final YAxis yAxis) {
+		this.yAxis = yAxis;
+	}
 }

pdb-ui/src/main/java/org/lucares/pdbui/domain/YAxis.java

@@ -0,0 +1,5 @@
+package org.lucares.pdbui.domain;
+
+public enum YAxis {
+	LINEAR, LOG10, LOG2
+}