Spectrum/Waterfall display zoom feature - work in progress (issue #33)

Implements zoom in/out by mouse scroll wheel and by right-click context
menu.

Still have to add ability to drag spectrum left/right when zoomed in.

src/spectrum/IDFTWidthChangeProcessor.java

@@ -0,0 +1,7 @@
+package spectrum;
+
+public interface IDFTWidthChangeProcessor
+{
+	public void setDFTSize( DFTSize size );
+	public DFTSize getDFTSize();
+}