Add copyright headers to all c/h files

[imciner2]

Since QDLDL is part of the OSQP source code, we should be explicit about the copyright and labelling of all these files. This will help tracking them during OSQP codegen, and if people use them separately.

The names in the files are based on the main contributors in the git history for them. I have also included the catch-all "OSQP Developers" to mean other contributors as well.

[coveralls]

Pull Request Test Coverage Report for Build 8939981067

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 8570611218:	0.0%
Covered Lines:	87
Relevant Lines:	87

---

💛 - Coveralls