build script simplification

- plotdevice/unpack.sh adds the app-specific changes to the source tree
- the `plod` dryice file builds our preferred subset of modules (if i
could figure out how to cleanly pass the opts dict to the default
dryice file that would be ideal, but i’m currently at a loss)
- `make install` assumes a repo called `plotdevice` as a sibling to the
`plotdevice-manual` directory