Lock preferences with a passcode (child mode)

[JasonSanDiego]

Is your feature request related to a problem? Please describe.
As a parent, I want to use Skytube to limit what my child can watch on YouTube. The existing allow list feature works perfectly for this but my child can change the preferences whenever he wants to allow more channels.

Describe the solution you'd like
Provide an option to lock the allow/block feature behind a passcode.

Unblock context menu item for channels in search would also need to be hidden when child mode is enabled

Describe alternatives you've considered
None

Additional context
None