Added support for building with Sencha Cmd on Travis-CI

- installs Sencha Cmd 3.1.2.342 in .travis.yml
- installs jsduck rubygem in .travis.yml
- executes sencha package build in .travis.yml
- sets up framebuffer and adds Firefox to Karma tests
- removes compiled JavaScripts from repository

In future pre-built releases will be available on the http://deftjs.org
website and as downloads on the GitHub releases feature. The GIT
repository itself will no longer be ready to use without Sencha Cmd.