Refactor EventContent

Use proper layouts and get rid of multiple annoyances/bugs like
text-wrapping randomly happening in the middle of words, background
rectangles being too large, a certain binding loop, etc

src/python/utils.py

@@ -44,6 +44,5 @@ def guess_mime(file: IO) -> Optional[str]:
 
 def plain2html(text: str) -> str:
     return html.escape(text)\
-               .replace(" ", " ")\
                .replace("\n", "<br>")\
                .replace("\t", "&nbsp;" * 4)