Travis: Using latest stable xctool rather than HEAD

Travis started choking when trying to `brew install xctool --HEAD`, complaining that `Error: xctool-0.1.7 already installed`.  Removed the `--HEAD` portion so that latest stable is installed, and if already install (as it seems is the case here) won't error.
Added Affero GPL v3 license

* Added LICENSE.txt with GNU Affero General Public License v3
* Added simple 4-line copyright and license doxygen-comment-style entries to the top of each file, just after the project name.
  > Used: find * -type f -exec sed -f ../sedscript -i '{}' \;
    where sedscript is: N; s`// Prototype 001`// Prototype 001\n// @copyright: Slipp Douglas Thompson\n// @copyright date: The date(s) of version control check-ins corresponding to this file and this project as a whole; or in lieu of, no earlier than 2013.\n// @license: The GNU Affero General Public License v3\n// \tA copy of the license can be found in the accompanying LICENSE.txt file; or in lieu of, see <http://www.gnu.org/licenses/>.`