allows apps to push users to the locale forwarder if app locale doesnt match the users choice

[andy-berry-dev]

Create a mechanism that (optionally) allows apps to push users back to the locale forwarder if the current app locale doesn't match the locale calculated from the locale cookie and browser headers.

This will allow users to refresh the page after changing their locale since after the refresh the locales wont match and the browser will be sent to the locale forwarder. It also means if locale pages are bookmarked the correct locale will ultimately still be used.

[andy-berry-dev]

This should maybe be a number of utilities on the locale service instead. That way the developer of the app can decide whether to immediately forward the user, ignore the difference in locale of display a warning.

We already have a mechanism for determining the preferred locale and the current locale. We probably want one more method to get the locale the user should be viewing.

[thecapdan]

failing test above should be for issue 802. can be ignored for this issue

[dchambers]

Now that #1186 has been done, we should add the extra requirement that LocaleSwitcher.switch() should work regardless of when it's invoked (i.e. it should be possible to invoke it from the app too, in addition to the locale-switching page), so that the following code should work:

require('br-locale/switcher').switchLocale('en');

for both types of multi-locale app:

1. Forwarding Style Multi-Locale Apps
2. Non-Forwarding Style Multi-Locale Apps

[thanhc]

tested locale switching with both forwarding and non-forwarding styles and both works, although found an issue with aliasing while testing this, raised #1268