Fix badge renumbering

Completely rewrites the badge renumbering functions.

The primary goal was to make badge auto-numbering work when badge shifting was turned off, as it was assigning duplicate badges in some circumstances.

Secondary goals were:
- making the function easier to read
- removing shift_custom_badges check from the shifting function and instead preventing the function from being called unless shift_custom_badges is true
- automatically renumbering badges back into their range, even if some badges of the same type are out-of-range
- keeping the logic about "which badge is actually considered 'next'" in the next_badge_num function, instead of tacking on adjustments after calling it
This block of code existed to handle cases where you assigned multiple badges within the same transaction.  How are you handling that case now?