Add copyright notices to source files missing them

[PetteriAimonen]

I have been asked by Rabbit Hole Computing to submit this pull request to clarify the copyright on files that I have written under contract to them. It didn't occur to me at the time to add the notices, even though it is generally recommended.

This pull request adds the notices to the source files that are my work. I consider that most of the headers don't have much copyrightable content in them. If you prefer, I can add the notices to them also for consistency.

Also if you'd prefer the full GPL license declaration at the beginning of the files, I can modify this pull request.

[PetteriAimonen]

Any updates on this?

[PetteriAimonen]

Rabbit Hole Computing has asked me to inquire whether there is anything that could be done to get this merged without involving lawyers.

[erichelgeson]

Rabbit Hole Computing has asked me to inquire whether there is anything that could be done to get this merged without involving lawyers.

RHC's lawyer emailed me on Fri, Apr 7, 2:13 PM CST regarding this PR that was opened April 5th, 1:21AM CST.

I've responded to the email from their lawyer and received no response back regarding this PR.

So to their question there is nothing to be done without involving lawyers as they have done so already just days after the PR was open. I will be closing this PR and locking it as there is no need to continue this via this forum, as RHC chose a different path a month ago.