Support direct text styling in collab mode

This is a pragmatic solution to support direct text styling (in ODF speak: automatic styles on text:span) in collaboration mode

Pragmatic, as it derives from the goal of having identic DOMs at all clients, instead it is okay with if the applied automatic styles yield the same styling results at all clients. It also is okay with leaving possibly empty (and thus useless) textspans behind, because while adding garbage it still results in usable documents.
This works for now, as no code/operations address the text:span or automatic styles directly. And due to that text:spans and automatic styles could be seen just as implementation details.

In some hopefully near future that will change, but for now this approach here seems to work.