Add option to delete all threads and replies by a user

[driesvints]

Add an option in the admin panel underneath users to delete all threads from a user. This is useful to delete threads in bulk while also banning them after they post spam en masse.

[tvbeek]

I was already thinking about this feature because it would be very useful 👍

[driesvints]

Was thinking about also adding it as an option when banning users to do it all in one go.

[franbarbalopez]

Opened a PR doing both, hope it helps!

[iam-subho]

Please confirm if this feature has already been implemented; otherwise, I will proceed to work on it.