Front-End Controller

This PR adds a front-end controller file implementing the main_interface.
It also adds template files for Prosilver, including the CSS and JS files needed.
Note: template files have been relocated from "all" to "prosilver".

The template files, styling and JS functionality are all ready and working.
However, they will require tweaking as we build up the controller file and
settle on template var names, and depending on any other changes we decide
to make or implement (i.e.: multi-level nesting of rules/categories).