New config and i18n modules.

This PR ports some improvements that I have done in other project in terms of i18n and config loading.

It includes:
- A new way to load config, instead of unknown coffee syntax, it uses json format that is much clear for almost all people. 
- `host` and `scheme` attributes of config are converted to `api` that is much clear to explain that it means. (this change are required also changes on urls and resource services)
- i18n service improved. Solved some bugs related to resource loading and make the directive name much shorter: `tr` (it makes put translation strings in templates more pleasant)
- Refactor of gulpfile for adapt it for new locales and configuration loading and port some improvements from other project.

I will start write deploy documentation with this in mind for make the next release with small documentation about how deploy it and how use taiga-scripts.

Finally it not viable for easy backporting to stable :(