Extraneous lines are output before some block macros because of empty paragraphs

Confluence puts some block macros inside their own paragraphs. It makes our generator listener sometimes output empty paragraph before those block macros.
We need to:

• make sure supportsInlineMode is correctly set on all our macro converters
• ignore the empty paragraph

This is not really a bug but more an improvement because the rendered result is correct, it's just that there are extra lines in the produced XWiki syntax.