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.
Frame can contain other frames with the text boxes.
This is something that has not been considered before
and meant that the whole construction of images was
broken in those cases. Also the captions were fixed/ignored.
