Adopt REUSE for Eclipse Projects

Let's investigate what it will take to have Eclipse projects adopt REUSE to make abundantly clear, as expressed on the REUSE website, "what license is a file licensed under, and who owns the copyright?"

I think that we're already pretty close. But some changes will be required:

• Adopt the use of SPDX-FileCopyrightText tags in file headers;
• Ensure that copyright and license headers are provided for all files; and
• Put license files in a directory named LICENSES.

There is some tool support to add headers and download license files, along with tools to validate compliance.

The requirement for copyright and license files for all headers, includes binary content (or other content that cannot otherwise include a header, e.g., JSON files). In these case, a .license file is added to supplement the file. e.g., a file image.jpg would have a corresponding image.jpg.license with header information.

As a first step, I'm going to see what sort of effort is required to convert one of the Eclipse Dash repositories to be compliant.

Note that adoption of REUSE should be compatible with the simultaneous adoption of SPDX Documents (see #46 (moved)).

/cc @mmilinkovich