This patch makes the attribute() and property() methods in KoGenStyle public instead of private. The main use-case for this class is of course only to set properies and attributes, then insert styles in a KoGenStyles and forget about the actual contents of the style, but sometimes when creating odf files it is useful to be able to later lookup properties of earlier generated styles, without having to double-store that information.
For example in the xlsx filter this is used because the cell style for merged cells is stored in one cell style in odf, but in the xlsx file it is a combination of properties from the cell styles for all cells that are merged. With this change I can simply merge the cell styles when I know that cells are merged, without having to keep the cell-styles around in another format than the KoGenStyle that already contains all relevant information anyway.