Change licence headers and add license file

1. Add a file with the complete GPLv3 license text which is required by the GPLv3 license.

2. Add copyright header to author declared files.

Pulls some author and date information from previous headers, adds this to information from the svn and git repositories. Include the standard copyright header to approximately 2000 files with institute of original committer as copyright holder. Contributing authors from previous declaration and repository records.

3. Changes from doxygen to plain comment

Decision to not use doxygen for licence headers. Removes doxygen formatting and file tag.

4. Cleanup license headers

Unify user names in the license header authors list. Remove duplicate users in the authors list. Cleanup of some other minor issues.