Attempt to read locale from localStorage key 'locale' first.

This allows for dynamic locale switching in the browser by setting the
'locale' value and refreshing the page:

Example (as described here: https://groups.google.com/forum/#!topic/requirejs/oKx6NQWtERY)
localStorage.setItem('el-gr');
location.reload();

Above code cannot be entered inside the mainConfigFile as it will
be considered invalid JSON by the optimizer.