When a piece of text has a text 'Source_Text' then
we assume that this is a piece of the document
that represents a code that needs to be inlined.
Addapted an odt writer to also reflect that change;
previously it was just writing a 'preformatted' text using
a non-distinguishable font style.
Code blocks are still not recognized by the ODT reader.
That's a separate issue.
