Update copyright headers to be generic

[dsmiley]

Some policies at the Eclipse foundation changed last year that allow the source headers to be more generic instead of requiring maintaining the individual contributors per file. If you look here:
https://www.eclipse.org/projects/tools/about.php?id=locationtech.spatial4j
We can change the first line (the copyright line) of source files to this:
Copyright (c) {date} Contributors to the Eclipse Foundation
Provided that our names are listed in the notice.md file.