Develop update

What's new?

• [CoverManager] Button to select(toggle) all front covers or back covers
• 🆕 [CoverManager] Added a button in CoverManager to process all the files without having to abandon the window.
• 🆕 Added option to toggle dark mode
• 🆕 Cover Downloader is back!

What's changed?

• [CoverManager] After processing, CoverManager will refresh all modified covers. (You can now keep deleting the covers until you run out of images 😛 )
• Clicking "Select files" or open folder will now not delete current selection if no new files were selected

• Fix some settings not saving and loading properly by @ThePromidius in #187
• Abort loading popup by @ThePromidius in #188
• Implemented Drag and drop for loading files by @ThePromidius in #189
• Cover downloader First implementation by @ThePromidius in #201

Full Changelog: v1.0.3...nightly_dccbbdd