Bug 141064 Remove group level data binding
This bug covers the engine part of the task to remove group level data binding. After the hange, all binding expressions will be defined on the table level, and each binding expression will have an AggregateOn field to explicitly define the group level for that expression.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
* a collection of all the queries
		 */
		protected Collection queries;
		/**
		 * the query stack. The top stores the query that is currently prepared.
		 * Needed because we could have nested queries
		 */
		protected LinkedList queryStack = new LinkedList( );
		/*
		 * report item query stack
		 * 
		 */
		protected LinkedList reportItemQueryStack;
		/**
		 * entry point to the report
		 */
		protected Report report;
		/**
		 * the execution context
		 */
		protected ExecutionContext context;
		/**
		 * create report query definitions for this report.
		 * 
		 * @param report
		 *            entry point to the report
		 * @param context
		 *            the execution context
		 */
		public void buildQuery( Report report, ExecutionContext context )