Markdown: rename MarkdownHelper to MarkdownUtil

Suggested in comments of Ib53e091617b39e22a230da9ec8a4aa39c3bf5c26
but rebasing it back that far in the series was just too many
merge conflicts.

Change-Id: Idc21fef22c6a7750c1bcb2b360ce3e973f3d23fb
7 files changed