My 30 subscriptions now take 25 ms to generate, instead of around 280.
Around 120 ms were saved by creating a database index.
Around 120 ms were saved by pre-compiling the pug template for video
description timestamps.
The other changes in this commit produced slight improvements.
Watched videos on your subscriptions feed will be darkened, and the
option to hide all of them has been added.
This only takes effect if you have enabled saving watched videos on the
server in the settings menu - default is off.