make directive able to be minified

Angular,  by default, infers the dependencies based on their names, but this behavior breaks when the directive is minified.

In order to be able to minify the directive, I had to annotate the functions with the names of the depedencies, the same way that the angular docs suggests to do in controller definitions. (See, [note on minification](https://docs.angularjs.org/tutorial/step_05))