update apksigcopier to upstream v1.1.0 (which adds support for gradle-signed APKs)

Replaces !1229 (closed) (and !1246 (closed) for now).

Closes #1051 (closed), though we could use more examples for testing.

v1.1.0 provides support for copying signatures from gradle-signed APKs.

We can typecheck apksigcopier (and the code that uses it) now that it has type annotations, so maybe we no longer want to exclude apksigcopier.py from mypy in pyproject.toml?

# exclude vendored file
exclude = "fdroidserver/apksigcopier.py"

cc @eighthave @jspricke