perf scripts python: exported-sql-viewer.py: Create new dialog data item classes

Create new dialog data item classes to replace SQLTableDialogDataItem.
This separates out different dialog data items and makes it easier to
add new ones. SQLTableDialogDataItem is removed in a separate patch
because it makes the diff more readable.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>