chore(dev): Bump grunt-contrib-watch to latest 0.4.x, enable livereload

With latest `watch`, the module contains builtin livereload.

* This enables live reload for each change of the sources or the demo files.
* A new virtual task `dev` is available which is actually only a shortcut for a) an initial build (w/o result) and b) a watch.

tl;dr:
1. (like before) Execute `grunt server` to start the express server, served on `localhost:3005`.
2. Ensure that your live reload plugin is active.
3. Execute `grunt dev` to start a fresh build (for demo) and implicity setup watch.
4. Any change to a source file in `ngTranslate/` or in the `demo` dir will invoke `jshint`, `karma` (currently the default one, this could/should be changed to a headless one, `copy:demo` and, obviously, `watch`.