Refactored core classes to accept base directory of application.

Previously they would always take in the exact directory they needed
(for example, the Config class would expect the exact directory
containing the configuration files).

Now they will all expect the base directory of the application. This
makes the code a little less portable, but does make things easier to
implement.
Add "global" helpers. First global helper is the translation module.

Global helpers are available to all views.

Specify the locale in the configuration tree under site/locale, and then
place all translations in flat JSON files in the src/locale/localename/
directory.
Fix regression error.

This change got lost when my repository got partially corrupted. It
causes the content of the page to be centred.
Updated readme file.