First push for #2: setup build process for github-pages

aim42 guide can now be created and pushed via the gradle wrapper command `./gradlew aim42 publishGhPages`. Unfortunately TravisCI integration will fail due to missing credentials - I'm working on this.

@gernotstarke The default branch in http://github.com/aim42/aim42.github.io/ needs to be changed to "gh-pages" instead of "master" for this to work. Only the repository owner can perform this change.