[Feature] Inhibit system sleep when scene is playing or tasks are running

[dumdum7]

Is your feature request related to a problem? Please describe.
The PC I run Stash on goes to sleep while I'm playing a scene on my phone/tablet. This happens because I have Windows set to put the computer to sleep after 30 minutes.

Describe the solution you'd like
Stash should prevent system from going to sleep while a video is playing or while tasks are running.

Describe alternatives you've considered
An alternative would be to inhibit sleep while a WebSocket connection is active.

Additional context
See how qBittorrent does this - they have an Inhibit system sleep when torrents are downloading option.