[FF] Classifieds Enhancements (+ Fixes) 1.1.9

A few useful extensions for NixFifty's Classifieds system - as well as any bug fixes that I spotted.

• Require prefix
  Adds a new option in the category edit page to require a prefix for posted items.

Linked prefixes
Link a classifieds prefix to a thread prefix - so the created thread can use the classifieds prefix, rather than just the category.

• Prefix filter under category
  List all the prefixes under each category in the navigation block that have items assigned.
  
  
  (Fiesta and Puma are prefixes, not categories)

FIX: Carousel image display
Correctly show the right number of items in the carousel (2 on mobile, 3 on everything else)

• FIX: Carousel navigation dots
  See above image.
• FIX: Price input as number instead of text
  Solves the issue with people entering "," as a thousand separator
  [Image unavailable; source: https://xenforo.com/community/attachments/1672835148013-png.279385/]
• FIX: Widen the left hand column display on wider screens so it's not all squished.

If you know of any other showstopper bugs in Classifieds let me know, I can look at fixing them in an update of this mod until @NixFifty releases his next version