Make a buildable source release

`tools/source-archive` creates and repacks the source release, and embeds ant and cmake version metadata in the release. `ant/version.xml` conditionally includes `ant/gitversion.xml`, overriding the use of git when building from a source release.  This file will never be present in a git source repository.

Testing:
```
ant release
```

Unpack the release (`artifacts/bioformats-5.1.0-DEV.zip`) *outside* the git repository.  All ant and cmake builds and tests should work without error in the unpacked source tree.  In the git repo, all existing ant, maven and cmake builds and tests should be unaffected.

Note that this is missing maven support.  The PR does not affect the existing maven build, but `mvn` will still fail in the source tree.  The `tools/source-archive` script may need updating to embed generated maven metadata if it can't use the existing `ant/gitversion.xml` metadata.  And the build needs to source and use the metadata, but I'm not sure exactly what to do here.