Move file operations (download/copy/move/delete) to background

[vauvenal5]

Moving file operations to true background will allow us to close the app after starting an operation. Also background support for download is important for bigger files.

[vauvenal5]

Open todos:

• [ ] cleanup managers
• [ ] improve notification text
• [x] fix ui behavior (Auto deselect on close)
• [ ] double check UI behavior in all cases
• [x] add global settings option to disable true background and use foreground prpcess