Add Never Spoil checkbox to html tracker

[Zymus]

Sometimes when using the HTML tracker page, you might go to check off Bank Reward #1, and in the process of moving your mouse over the checkbox, accidentally hover over Bank Reward #2, and spoil yourself on the reward.

This adds a Never Spoil checkbox near the top of the page, that works in light mode and dark mode, that prevents the spoilers from ever showing. Even if you check the item off, it will not show the spoiler, until the Never Spoil checkbox is unchecked.

[ZoeyZolotova]

I like the idea. I understand the use case for not revealing spoilers on hover, but what's the use case for not revealing checked-off spoilers?

Might it be a better solution to change the :hovers to :active so that the mouse has to be held down on the spoiler to reveal it. And we can leave the revealing of a checked item as before?