Bug 136571 Drop property is displayed in Property Editor for all kinds of cells.
Description: Drop property displayed in Property Editor for all kinds of cells. Drop property is only supported by cells in group but it is listed in every kinds of cells even in grid cell which will mislead users.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/SimpleGroupElementHandle.java
Object item = elements.get( j );
			if ( !( item instanceof DesignElementHandle ) )
				return Collections.EMPTY_LIST;
			List propDefns = ( (DesignElementHandle) item ).getElement( )
					.getPropertyDefns( );
			if ( propDefns.size( ) < min )
			{
				min = propDefns.size( );
				rtnPropDefns = propDefns;
			}
		}
		return rtnPropDefns;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.api.GroupElementHandle#isSameType()
	 */
	public boolean isSameType( )
	{
		if ( elements.size( ) == 0 )
			return false;
		IElementDefn baseDefn = null;
		for ( int i = 0; i < elements.size( ); i++ )
		{
			Object item = elements.get( i );
			if ( !( item instanceof DesignElementHandle ) )
				return false;
			IElementDefn elemDefn = ( (DesignElementHandle) item ).getDefn( );
			if ( baseDefn == null )