.back-button lacks arrow

[hanaral]

Old stylesheet:

New stylesheet:

[cassidyjames]

Yep, as expected at this stage. The arrow style we did before has to be provided as an SVG that perfectly matches the final GtkCSS styling, and since the latter is in flux, it doesn't make sense to try and keep up with a hand-crafted SVG. Ideally we could use Granite to actually custom draw a back button, but I'm not sure if that's the concrete plan or not.

[hanaral]

Alright, I assumed the SVG wasn't done yet (I will admit I did fear that it might be going away)