NGI0 - Updating licensing aspects according REUSE

[Potherca]

Hello, I would like to propose some updates regarding copyright and licensing information. REUSE specifications intend to make licensing easier by setting one way to display all this legal information through comment headers on source files that can be human - and machine – readable. Feel completely free to adopt these specifications by merging this pull request.

REUSE Features:

* SPDX copyright and license comment headers for all relevant files

* LICENSES directory with all licenses used on the repository

* Licensing of image files (please be aware that I licensed the image file under the MIT license, but you can also use another license, in this case please do not forget to add the selected license text to the LICENSES folder that I have created within the repository)

Files missing copyright and licensing information:

I added the comment headers with copyright and license information to some of the files that lacked that information. Please take into consideration that some files such as ".list" were not modified. However, we suggest to license these files under the CC0-1.0 license. (in this case please do not forget to add the selected license text to the LICENSES folder that I have created)

I provided license information to README file as well.

Please also double check if the personal information in the headers is correct and consistent

No contribution policy:

We have noticed that your project does not have a contribution policy. Therefore, we strongly recommend you to implement one. To get further information about this please check our documentation: https://download.fsfe.org/NGI0/V2/FSFE%20-%204%20-%20Free%20Software%20Contribution%20Policy.pdf

Further REUSE compliance

In case you find REUSE useful, we offer a wide range of tools to help you to continuously check and display compliance with the REUSE guidelines.

Hope that helps and thank you very much for the amazing job!

Originally reported in https://github.com/pdsinterop/solid-nextcloud/pull/29#issue-754244463 by @lnceballosz

The original pull-request is closed as it could not be used as-is. This ticket serves as reminder that the task still needs to be done.

Currently there is an issue with PHP in the REUSE tool (see https://github.com/fsfe/reuse-tool/issues/436) which means the task can not (yet) be automated. Once that issue is resolved, this ticket should be revisited (as well as implemented in other PDS Interop Repos).

[Potherca]

The related REUSE issue has been resolved, so this can be worked on.