A TableSource is introduced which is used to manage all tables as name/model pairs. The CellRegion is changed
to store a Table* pointer ("handed out" by TableSource) instead ot just the sheet name.

The ChartProxyModel is adapted to accommodate these changes. ChartProxyModel::slotRows/Columns/Inserted/Removes()
are obsolete, remove them. Another commit will change the ChartTableEditor to take care of handling removals
and insertions in the internal data table, as this is to be handled as a special case.

Various test cases have been written to cover these changes and are in this commit or will be committet later.

See http://svn.reviewboard.kde.org/r/5373/

svn path=/trunk/koffice/; revision=1176523