Keep the glyphs in SVG format and build the font using a FontForge
script.
A part of the previous font is kept because the sources is lost.
This adds a new dependency to the build system, fontforge.
The ant scripts included in the android SDK were removed recently. The
alternative is Gradle.
Gradle doesn't work well in this app because it's not possible to use
Nix to pull dependencies. Gradle will try to patch the SDK.
Also, it's very slow.
It turns out the required build script is quite simple.
