Clean up and refine serial note support, part 2

Clean up and refine serial note support, part 2

Because of the way our notes are being rendered, a handful of
special XML characters can break the note interface when editing.
These characters are now properly encoded as entities.

Also, editing of newlines presents a similar issue with different
consequences, and it is handled similarly but separately.

Signed-off-by: Dan Wells <dbw2@calvin.edu>