Move StyleTag to StylesEntry

[jferard]

The StyleTag XML is written in content.xml > automatic-styles. That's the wrong destination, since FastODS does not allow anonymous styles. The output has to be moved to styles.xml > styles.

[jferard]

There are a lot of problems with that commit:

• LO does not recognize common styles for rows, columns or text spans.
• LO does not accept text family styles for page layout if those styles are not in Styles/automatic-styles.
• A few other limitations.

A good rule of thumb: follow LO if possible, even if LO does not fully respect the specs.

[jferard]

Fixed with the StylesContainer class, which centralizes the style definitions. Entries use it to write styles XML in the suitable place.