Generate code documentation from source-code doc-comments

Adds a "docs" tasks to the Ant build configuration which generates source-code documentation from doc-comments as a static web site via Javadoc.

Adds missing doc-comments for packages, classes, and methods, although often incomplete or simply copied over from the Beast2-style @Description annotation. Also some stylistic changes: breaking long lines, remove trailing white-space, etc. Some extra code comments to improve code readability. Renames the lumiere.model package (back) to the less generic lumiere.fitnessmodel.