Add YottaDB copyrights to almost every file in the repository (except extensions ".ref .rst .png .zwr .html .ci")

A few .txt files (e.g. T0001.txt) were renamed as .ref to indicate they are a reference file.
The .ref file (e.g. T0001.ref) is not copyright checked but .txt files are (e.g. CMakeLists.txt)