Coffee build before publication on NPM

* added Cakefile with
    * linter
    * build coffee to JS
    * clean JS files

* in dev mode, you don't need js file but you will have to use bin/cozy-dev
* when npm publish, the following happens:
    * cake build
    * package is published
    * cake clear-js
That what you never have to worry about JS file polluting your development environment.

* minor improvement: cozy --version command takes its data from package.json

Fix https://github.com/mycozycloud/cozy-manager/issues/21