[CUSTDB-804] Better handling of user delete#319

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battye wants to merge 2 commits intophpbb:3.2.xfrom battye:feature/user-delete-handling

Commits on Aug 1, 2020

Add listeners for user deletion with functions to delete contribs, CDB posts and CDB topics
battye
committed

Commits on Aug 2, 2020

Limit post/topic deletion to the Titania support type
battye
committed