Fixes several errors such as:
104) UserRegistrationsController via ajax sets user.locale from cookie on create
Failure/Error: I18n.locale = spree_current_user.andand.locale || cookies[:locale] || I18n.default_locale
I18n::InvalidLocale:
"pt" is not a valid locale
# ./app/helpers/i18n_helper.rb:14:in `set_locale'
# ./spec/controllers/user_registrations_controller_spec.rb:56:in `block (3 levels) in <top (required)>'
Why:
* Starting the environment, even with just `bundle exec rake`, results
in the following error:
```sh
Value assigned to config.time_zone not recognized.Run "rake -D time"
for a list of tasks for finding appropriate time zone names.
```
This change addresses the issue by:
* Adding the time zone setting to environment specific configurations,
defaulting to UTC in development, and using Melbourne in tests.
Since `en` is considered as the main fallback for all locales
ensure that it is present in all environments.
Note: Setting `config.i18n.fallbacks` to `true` means use the default locale
which means that if a particular instance is not using an `en` based locale
(the parent `en` locale is automatically derived as a fallback) then `en` will
not be available as a fallback.
