Feature/soft deletion cmp na 000025

@neil.crossley can you have a look if this is now sufficient for cmp.na.00025?

Not that there is a feature change included. Timed out sessions are only deleted softly (set to terminated state and deleting related data). Imho this better fits the text in cmp.na.00025. However this also means, that sessions, independent of successfully finished or timed out, stay in the system until the long retention period for terminated sessions is over.

@prechtlm if @neil.crossley approves, feel free to merge to your test branch.