Add font selector; load all fonts from fonts/ directory; bump to 0.85

All .ttf files in fonts/ are loaded at startup. The web form now has a
font selector dropdown. Glyph-rendering helpers that previously used
module-level font globals now accept a _FontData parameter threaded
through from generate_svg().

Dockerfile updated to copy all of fonts/ into the image rather than a
single hardcoded .ttf path.

k8s/deployment.yaml

@@ -15,7 +15,7 @@ spec:
     spec:
       containers:
         - name: m1730-generator
-          image: git.baumann.gr/adebaumann/m1730-generator:0.84
+          image: git.baumann.gr/adebaumann/m1730-generator:0.85
           imagePullPolicy: Always
           ports:
             - containerPort: 5000