Bug 152828 Add the projectFolder property on module
When user doesn't set the resource folder path in designer, there should be a default working path for Birt to manage the report design and find the related resources. A new property should be added on Module: name: projectFolder type:URL This property only can be given from the open design method from session but should not be set after the module initialized. Concern about the backward compatiblity issue, a new method will be added. Open design with a config argument.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignSession.java
/**
	 * Removes a report design from the list of open report designs.
	 * 
	 * @param module
	 *            the module to drop
	 */
	public void drop( Module module )
	{
		if ( module instanceof ReportDesign )
		{
			assert designs.contains( module );
			designs.remove( module );
		}
		else if ( module instanceof Library )
		{
			assert libraries.contains( module );
			libraries.remove( module );
		}
	}
	/**
	 * Returns the application units. The return value is defined in
	 * <code>DesignChoiceConstants</code> and is one of:
	 * 
	 * <ul>
	 * <li><code>UNITS_IN</code></li>
	 * <li><code>UNITS_CM</code></li>
	 * <li><code>UNITS_MM</code></li>
	 * <li><code>UNITS_PT</code></li>
	 * <li><code>UNITS_PC</code></li>
	 * </ul>