When changing sort mode in a thread, highlights are lost

[aesy]

Potential solutions:

• Track last thread and don't update visit timestamp if current thread is the same as the last. Why good: Easy to implement. Why bad: Would make it so that refreshing a page to see new comments wouldn't work anymore. Could also track sorting mode to circumvent this.

• Save multiple thread visit timestamps and let user pick which to use for highlights. Why good: Flexible. Why bad: Tedious to implement. Would require injecting UI components and reevaluating highlights.