Update SRF 'format=graph' to use GraphViz extension version 1.1+.

Also update SRF composer.json to suggest mediawiki/graphviz.
> to other objects

??? The only difference is in the function scope. I prefer using $GLOBALS, though in this case it is the last of our worries, and `global $wg` is used all over the place anyway. So I'd not block this commit on that