Still needs some work to:
- Minimise AJAX calls by writing multiple settings at once.
- Move the settings storage/retrieval JS code into a global file
- Avoid using synchronous AJAX calls in the main thread
This adds bootstrap-dialog to help with creation of nice dialogs,
and adds the ability for modules to render Javascript into the
browser, and specify onclick handlers in the menu system.
Also add a basic About dialog, using the new infrastructure and
showing some useful info about the application.