Add copyright headers

Dear @jhimanen ,

We analysed the current code and found that the copyright headers were missing from your source code files under this repository "policy-library". We have produced this Merge Request to add the headers to a few files where the copyright header was missing.

We invite you to check each change because there are some cases in which the addition of the header can create issues, like in files which are input for another process and we are not sure if comments or a header are expected. Please have a look at them.

You will find the last section of the header called Contributors. There, the developers are expected to add their name and contribution. For example "Joel Himanen - Author", "XX - Coauthor", etc.

Feel free to be inspired and/or accept the whole Merge Request.

Thanks.

/cc @asgomes