don't created vestigial frame canvas item for TimeAxisViewItem unless actually needed.

They don't cost very much but there's just really no point cluttering up the scene graph with generally invisible
and insensitive items
when drawing only part of a Canvas::Rectangle outline, we only need to do the cairo-pixel alignment math for the axis perpendicular to the edge
fix up dimensions of ghostregion colored rect
simplify removal of outline from automation time axis base rect
simplify removal of outline from streamview base rect
remove TimeAxisViewItem::RIGHT_EDGE_SHIFT; fix up x-coordinate for right edge of an audio fade out