Update Licensing

[PhoneDroid]

Changes

• Added SPDX license identifiers
• Added SPDx file notices
• Updated copyright headers
• Use proper license setup

[yorikvanhavre]

This actually changes the text of the license (Program -> Addon). I don't know if that's a safe thing to do...

[PhoneDroid]

@yorikvanhavre As long as it doesn't change the meaning, there shouldn't be a problem, nothing about the rights granted nor the conditions is changed.

[howetuft]

I agree with Yorik and I will add:

• SPDX is redundant with current licensing headers. So it's either one or the other.

• The proposed SPDX headers are not acceptable as a full replacement of current licensing headers, as they do not mention copyright grantees and authors (namely, Yorik and I)

[PhoneDroid]

@howetuft

SPDX is not the same as a license header, nor is that redundant.

SPDX license identifiers are a standardized machine readable format that declares the license of a file, copyright headers are a freeform summary of ones rights.

Personally I prefer using SPDX only, copyright headers are after all not actually necessary in the face of the actual license file, however many people go with the FFS current recommendation of having both.

There are no SPDX headers, nor am I attempting to replace copyright headers with SPDX here.

[PhoneDroid]

https://freecad.github.io/DevelopersHandbook/codeformatting/Copyright