Support for sgtitle

[ThexXTURBOXx]

When using a tiled layout, the super-title from the sgtitle command is not yet translated to TikZ.
One solution to make this work in TikZ is to manually add the following snippet at the end of the tikzpicture:

\node[above,font=\large\bfseries] at (current bounding box.north) {\shortstack{Some title\\even with multiple lines}};

Of course, there are more possibilities to achieve this, but that seems to work rather well, with a small caveat:
The title is centered with respect to the entire figure and not only the axis environments (if there is a legend to the very right of all the subplots, e.g., using the approach from #1128, the super-title will also be affected).
There are ways to work around this, but they apparently need the positioning tikz-library to work.