Licence & copyright

A script has been created ( replace_header ) to handle the replacement of copyright and license header in all source files.

It correctly replaces .py headers.

For .h, .c/.cpp, .css and .html it will add a new header in the beginning of the file even if it has a header already. Human verification is needed after applying the script on these files. It is done like this because it seemed to me that the effort of developing a multi-line comment parser was bigger than revising the few exception files by hand.