Bug 188578 Add "displayColumnName" on TabularLevel
Add Property "displayColumnName" on TabbularLevel and corresponding APIs on handle. Property Type: expression.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/olap/TabularLevelHandle.java
implements
			ITabularLevelModel
{
	/**
	 * Constructs a handle for the given design and design element. The
	 * application generally does not create handles directly. Instead, it uses
	 * one of the navigation methods available on other element handles.
	 * 
	 * @param module
	 *            the module