[Homebrew feature improvement] Allow multiple slots for the same level with campaignFeatSections

Currently you can only define unique levels per slot in the campaignFeatSections objects. E.g. This is allowed: `slots: [1, 2, 3]` But this isn't currently possible: `slots: [1, 1, 1]` The latter does display correctly in the sheet, but in the dom each `<li>` slot gets the exact same data-slot-id, so the drag & drop behavior doesn't work correctly. (if a single slot is already taken, any new item dropped shifts to the Bonus Feats section. --- Low prio feature request. I currently have a workaround to **_not_** set any `slots` at all. That way you can drag infinite amount of items on the feat category.