Multiple fixes: pango, subscripts etc

The label rendering changed from 'toy' API in cairo to proper
pango-cairo usage.
https://bugzilla.gnome.org/show_bug.cgi?id=612371 (partially, no change
handling yet)

The subscripts are used for variants of the same layout,
https://bugzilla.gnome.org/show_bug.cgi?id=613853