refactor database class hierarchy

plugins/com.minres.scviewer.database/src/com/minres/scviewer/database/DoubleVal.java

@@ -0,0 +1,26 @@
+package com.minres.scviewer.database;
+
+public class DoubleVal implements IEvent {
+
+	final double value;
+	
+	public DoubleVal(double value) {
+		this.value=value;
+	}
+
+	@Override
+	public EventKind getKind() {
+		return EventKind.SINGLE;
+	}
+
+	@Override
+	public Class<?> getType() {
+		return this.getClass();
+	}
+
+	@Override
+	public IEvent duplicate() throws CloneNotSupportedException {
+		return (IEvent) clone();
+	}
+
+}