Config files and checkpoint not included in 1.0.3 release

**Describe the bug**
The config files in `mattergen.conf` and the checkpoints and other data files are currently not included in the v1.0.3 release on PyPI.

**To Reproduce**
```
pip install mattergen=1.0.3
mattergen-train
```

**Expected behavior**
Include config files by default using `MANIFEST.in` or by specifying the setuptools package data entries.