Footer stucking to the viewport fix and MultiSlide feature for Fordson

[FloeHetling]

Greetings!
Here's a brief overview of changes:

Fixes:

• #page-wrapper CSS class now has presence in Fordson SCSS. That fixes invalid footer behaviour (sticking mid-page on long pages)

Features:

• User can now adjust quantity of slides in the main slideshow via Moodle Admin Settings pages for the Fordson theme
• User can now hide slideshow from unregistered users
• Slide image can now be supplied with a hyperlink to some internal or external web page.
• Minor code optimisation to make it more scalable.