Add support for custom device-tree files, and applying overlays to them.
This is useful for supporting non-discoverable hardware, such as sensors
attached to GPIO pins on a Raspberry Pi.

In response to comments, create a sub-folder for deviceTree packages
(starting with rpi), and a top-level package for helpers.

This is just as messy as it is for the kernel files. Maybe it should be
done in the uboot boot-loader?

Signed-off-by: Sascha Grunert <sgrunert@suse.com>

podman: 1.4.4 -> 1.5.1

CNVkit: init 0.9.6

bitcoin: 0.18.0 -> 0.18.1

snscrape: 0.2.0 -> 0.3.0

The shebang in the python stub template was incorrectly patched to
```
<store-path>/bin/env python
```
instead of
```
<store-path>/bin/python
```

The reason was that `patchShebangs` was called with `--replace` which is
an unknown argument.
```
patching script interpreter paths in src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt --replace /usr/bin/env python /nix/store/w7gsq8v86hni4ynaqgwwlnlny115ylng-python3-3.7.4/bin/python
find: unknown predicate `--replace'
```

Using `substituteInPlace` instead resolves that issue.

The wrong shebang caused failures of `py_binary` targets due to `python`
not being in `PATH` in certain circumstances.

nixos/hardware.deviceTree: new module