Added Dark Mode, a few other changes.

Changelog:

Added a button in the upper-right corner allowing users to switch to Dark Mode, an inverted version of the color scheme.

Doing this in a way that doesn’t annoy people requires saving a variable in your web browser, so I’ve also added a one-time “Cookie Law” warning about that that appears at the top of the page the first time you use it. If you want, you can read a detailed explanation of how it works here. The short version is that the site still doesn’t track you in any way. This is just so people using Dark Mode don’t have to switch it back on every time they turn the page.
Switched the main page table of contents to appear in chronological order, with the oldest episodes first. You can still click “Reverse Sort” if you want to see them the other way around.
Fixed broken links on the Sources page and edited the design a little.
Made Ebook download link and Search link in top navigation bar display as icons on mobile devices.
Edited the way the spoiler-code Javascript that hides the episode content warnings lists gets inserted; removed two utility pages that I hope no one but me was using (‘feed.json’ and ‘sources_auto.html’); and a few other backend changes that shouldn’t be visible to anyone else.