Update all copyright notices to AGPL v3 License. Closes #4.
After online discussion at 07/07/2011 through mail, all contributes agreed
to relicense the software to AGPLv3. This is done as AGPL is more appropriate
license for network services software.
Also authors where moved out of the copyright headers and an AUTHORS.txt file
was introduced. This will help focusing on actual development and welcoming
new members.