Po-projects

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* Better layout and ergonomy on all ressources;

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* Better Catalog create form on project details page;

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* Better translation source rendering in the translation update form;
* Remove the Project's slug field from the project update form;

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* Add a more ergonomic interface for translation form with sticky fixed menu, translation statistics and a more readable layout;
* Add 'domain' attribut on Project model so now projects have an explicit domain name to use for write PO catalog files;
* Force gettext domain in forget Babel catalogs;
* Move forms and add crispies;
* Add assets for django-asets;
* Add Compass stuff to build SCSS;
* Add static files;