Disable font icons

[Riduidel]

Font icons usage should be deactivable at will in generator code.

Indeed, when publishing to confluence, font icons are replaced with

See on <ac:image ac:alt="github"><ri:attachment ri:filename="github"></ri:attachment></ac:image> GitHub

And this fails to upload, since the generated file doesn't exist on Confluence side.

As long as confluence-publisher/confluence-publisher#228 is not solved, we will have to have a toggle on our side