[Feature request] Try to prevent sleep while downloading

[fidel]

In case media-dupes is currently downloading it should always try to prevent the device to go to sleep.

See:

• https://www.electronjs.org/docs/api/power-save-blocker
• https://ourcodeworld.com/articles/read/539/how-to-prevent-that-the-system-enters-in-suspension-sleep-mode-in-electron-framework

[fidel]

Case 1: Downloading starts - should enable powerSaveBlocker
Case 2: Downloading finished - should disable powerSaveBlocker