Gray out contents of the Note tag

To make it easier to differentiate between notes and actual markup, it might be useful to gray out the contents of the Note tag (maybe even the tag itself) similar to how HTML comments get grayed out. If there are tags within the Note tag, this would also allow those tags to clearly appear as a note and not as actual running markup.

As requested by @RichardC in the forum thread discourse.tangible.one/t/possible-improvement-for-note/789