Background: Clients write Markdown and convert it to HTML before
sending the event. All events are formatted as HTML. However, if an
HTML formatted event happened to include markdown characters, Element
Android would incorrectly render that markdown.
For example, an event with formatted_body: "*test*" should be
displayed as literally *test* with no effects, but Element Android
incorrectly displayed it as test in italics.
This commit fixes this behaviour, making Element Android not parse
Markdown in HTML messages.
From the perspective of most users it will appear that backslash
escapes now work properly (even though this wasn't the real issue).
