Add ability to downvote feature suggestions in the roadmap. Might enable better prioritisation of community demand.

Reasoning: In the current set up, 15 people might want a feature whilst 50 might hate it. But it will show as in high demand (because of 15 upvotes). Whilst another feature with 15 upvotes as well migth be hated by none, but it will currently show as equivalent (because of 15 upvotes).