records: enriched file headers with license statements

[tiborsimko]

Looks good, just needs to be up to date with upstream master... Please rebase like this:

$ git remote add upstream git@github.com:cernopendata/cernopendata-client
$ git fetch upstream
$ git checkout master
$ git merge --ff-only upstream/master
$ git checkout 11-gt-fix
$ git rebase master -i
$ git push origin 11-gt-fix -f

similarly to https://github.com/cernopendata/opendata.cern.ch/blob/master/DEVELOPING.rst#updating-pull-requests