fix: mark premiere videos as unplayable

[SethFalco]

Previously, if a channel, search result, or feed, featured a premiered video that was still upcoming, the Invidious add-on would show it like any other video, but would throw errors when trying to play it.

There was no indication in the UI that it's a premiered video.

This PR makes three changes:

1. If a video is marked isUpcoming in the API, it makes the video unplayable.
2. If the video has a premiereTimestamp, display that in the subplot instead of the view count and publish date.
3. Make the UI for date times locale and timezone aware.

Screenshots

A feed that includes a channel with an upcoming video. The subplot text of a upcoming video shows "Premieres: " instead of the view count and publish date. Locale is en-GB and timezone is Europe/London.

Same screenshot as above, but with my system timezone locale set to en (probably defaults to en-US) and timezone set to New Zealand.

A channel with an upcoming video. Locale set to en and timezone set to Europe/London.

Information pane is opened while focused on a video.

Now that the example video has already past the premiere date, it shows up like any other video and is playable.

Notes

• You'll see the order between the feed and channel videos differs. On YouTube, a channel will show videos in the same order we do. However, I don't have a YouTube account, so in the feed I don't know if we're showing videos in the same order as the YouTube subscription feed does.
• I had trouble using __date__ (which afaik delegates to __transform__ internally) because the premiereTimestamp is a conditional attribute. script.module.iapc was throwing exceptions for videos that didn't have it, so I opted to handle transforming it in this plugin.
• I originally planned to use relative time to display when the video would premiere, but I opted to follow the YouTube interface, which shows absolute time. However, we need to be timezone aware otherwise users will be confused.
  • Either the user lives ahead of UTC, so the video still wouldn't be available even after the time passed.
  • Or the user lives behind UTC, and will wonder how they got late to the party even though they showed up "on time".

References

• Kodi documentation for regional interface settings

[SethFalco]

Context:

Directive	Meaning	Example
…	…	…
%x	Locale’s appropriate date representation.	08/16/88 (None); 08/16/1988 (en_US); 16.08.1988 (de_DE)
%X	Locale’s appropriate time representation.	21:30:00 (en_US); 21:30:00 (de_DE)

— Excerpt from Python documentation for format codes.