EZP-23199: As a developer, I want to be able to override and add new Handlebars templates

JIRA: https://jira.ez.no/browse/EZP-23199

# Description

As the title suggests, this story is about changing the Handlebars templates handling so that it's possible to inject custom templates or override the existing ones.

# Tasks

* [x] Get some reviews on the document
* [x] Write the custom controller to automatically wrap the templates in a YUI module
* [x] Change the `Y.eZ.TemplateBasedView` to use the template registry
* [x] Moved the Handlebars templates to use the new module system
* [x] Handle the case of the partials
* [ ] ~~Write the dump script~~ (will be handled in a separate PR/issue)
* [ ] ~~Pre-compile the template before dumping to the disk~~ (will be handled in a separate PR/issue)
Don't add default values in siteaccess based config. Use `default_settings.yml`