Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DimensionConditionHandle.java
*/
	public DimensionConditionHandle( SimpleValueHandle valueHandle, int index )
	{
		super( valueHandle, index );
	}
	/**
	 * Gets the list of the primary keys in this dimension condition. Each one
	 * in the list is instance of <code>String</code>.
	 * 
	 * @return a list of the primary keys in this dimension condition if
	 *         defined, null if not set
	 */
	public List getPrimaryKeys( )
	{
		return (List) getProperty( DimensionCondition.PRIMARY_KEYS_MEMBER );
	}
	
	/**
	 * Adds a primary key to this condition.
	 * @param key
	 * @throws SemanticException
	 */
	public void addPrimaryKey( String key ) throws SemanticException
	{
		MemberHandle memberHandle = getMember( DimensionCondition.PRIMARY_KEYS_MEMBER );
		memberHandle.addItem( key );		
	}
	
	/**
	 *