bower_components directory shouldn't be watched

From #14 

Grunt now "watches" html files only in the root directory of the app or in the "templates" directory. This should increase performance, because grunt won't watch the ```bower_components``` directory anymore. (https://github.com/gruntjs/grunt-contrib-watch/blob/3ec9cd8d7f91262ddb713a2f0968eb08067135b3/README.md#why-is-the-watch-devouring-all-my-memory)