Create debian & rpm packages.

`debian:packageBin` and `rpm:packageBin` create `scala-$version.[deb|rpm]` in `target/`

- subdirs not requiring special treatment are rooted under `installTargetUnix.value`
- docs go to `installTargetUnixDocs.value`
- create symlinks under /usr/bin/ for all scripts in `installTargetUnix.value / "bin"`
- make scripts in `installTargetUnix.value / "bin"` executable, drop ".bat" files
- map man to /usr/share/man/
- map doc to `installTargetUnixDocs.value`
- map api to `installTargetUnixDocs.value / "api"`
Standardize msi's name.
Discontinue packaging of tool-support.

Hopefully someone will take over maintenance, or we will when demand arises.
s3-upload support, and cleanup

Only load Wix settings when on Windows,
do the rest of the work when not running on windows
(packageBin in universal, universal-docs, debian, rpm)
Update README.