Whenever a textbox block title was changed, the html artefact inside
it also had its title changed.  That was confusing, so instead we're
going to set the html artefact's title once, when the textbox is first
created (generating a title for it if the block has no title).  Once
the html artefact has been created, the title can no longer be modified
from the view editor again.  However, the ability to update the artefact
title from the notes area is added, so that the user can keep the title
in sync with the block titles if they want to.

Change-Id: I98e2529e7c81759c9b22130da355e227c8f3d577
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>