Feature/multilanguage support

### Multi-language support for Copay

* Using gettext-bower (http://angular-gettext.rocketeer.be) for generate POT file.
* Angular gettext plugin for compile a translated PO file inside a new file: "translation.js".
* Default language is English (in config.js), but you can change it in Settings.
* Spanish translation of Copay. Need review (and probably corrections).

### How to use (for development)

1. Follow this text to add string to translate. (http://angular-gettext.rocketeer.be/dev-guide/annotate/). If you need translation from any javascript files, use a dummy file: dummy-translations.html
2. Run "grunt translate" to generate POT file.
3. Open po/es.po with Poedit (or another PO editor) and UPDATE from .POT file.
4. Translate and save.
5. Run "grunt"

### How to use (for production)

As the PO file is hosted on github, it is only necessary to do (to generate translation.js file):

```
grunt prod
```