There are the following issues with the current implementation:
* `fetchurl` with a tarball from GitHub appears to break occasionally
because the tarballs are not necessarily reproducible. Because of
that, `fetchFromGitHub` unpacks the tarball already because the
contents are actually reproducible in contrast to the tarball. To have
the same behavior here, we use `fetchzip` now (and `applyPatches` on
top to apply additional patches if needed).
* Fixes the way how patches are applied. Previously, when having patches
for a git checkout of the app, these wouldn't apply because the
`appname-version` prefix is missing.
* Because all old hashes are broken with this, I added an evaluation
check that breaks evaluation when using the old API (i.e. with
`name`/`version` which are not needed anymore).