Add instance name to font label

[RoelN]

https://user-images.githubusercontent.com/45946693/68811490-c620d180-063e-11ea-814d-e5c74110c983.png

Also see https://github.com/arrowtype/type-x/pull/72#issuecomment-553642957

[arrowtype]

I think this is already working, right...? Or, is there something here that isn’t yet working as expected?

There might be opportunity to further improve the font override naming system, but I’ve made a separate issue for that.

[arrowtype]

I think this is already done – if you agree and there isn’t something you feel is still missing here, @RoelN, please feel free to close it.

[RoelN]

After some more testing, it works the first time the extension is turned on, but breaks after closing and re-opening the extension :-( So this should be investigated. (This can de done in parallel to the name override story)