Downloads as background processes

[breech]

Currently LB locks down the UI during download processes. Could we have an option to download updates/metadata/DB content in the background? This is always time consuming and disruptive (Update from 6v12 to 7 took about 10 mins, metadata another 2).

Suggestions:

• Option to download silently so updates can be applied on the next restart.
• When finishing editing a game but still downloading DB content, the game image could be replaced with a placeholder to indicate that content is pending.
• Diff patching could help to reduce download size/time, and server load.

[fraganator]

Issue #2156 was marked as a duplicate of this issue.