Making Quassel slowly ready for its first release...

- Fixed all license headers so that they look consistent;
  we also now allow GPL v2 and v3 (but no blank "or later" option)
- Added new and edited old READMEs and INSTALLs and stuff
- Added the texts of the GPL v2 and v3 as required

Ok, so that should take care of the legalese, now we have to polish the code... :)