ExtendedDataTable component description adding to the guide
the component is added, language and syntax is checked
now it's necessary to verify the content and format to meet all our other components descriptions.
add note that this component is released with preview marker
1. The note is added.
2. The component works due to description given in guide (checked on sample trunk\samples\extendedDataTable_sample).
3. All images are brought to 96 dpi resolution and corrected.
rowKeyConverter, activeRowKey and groupingColumn attributes are described