Added ALLOWED_HOSTS configuration for Django

As it's part of the default django settings, we also need this in mezzanine
Python 2/3 fix for forms export.
Merge
Added LANGUAGES to settings, since they're needed for multilingual support
Added django.middleware.locale.LocaleMiddleware to MIDDLEWARE_CLASSES
Added i18n_patterns and apply it only to admin sites
Added a language selector field to the login and admin site
Mention Widgy in the list of third-party modules
Only show admin language selector when multiple languages configured.
Merge
fix cn translation for "Page not found"
docs: fix some typos
Don't use future's int for int settings. Closes #855.
Merge
Merge
Added Leo Zhu and Hervé Cauwelier to AUTHORS
Add translation hook to settings file.
In admin customization section of docs, mention in_menu method on admin classes for controlling ADMIN_MENU_ORDER behavior.
Move requirements file for project_template into project root to better conform with hosting providers like Heroku. Closes #859.
Typo