Manually activate user account (Admin feature)

[AdrienneMendrik]

Is your feature request related to a problem? Please describe.
It happens in some occasions that people who try to create a Next account do not receive the activation e-mail, and therefore cannot activate their user account.

Describe the solution you'd like
Add a option in the admin screens on Next to activate an account manually (confirm in db), next to verify? In this way support staff can activate a user account when someone contacts support.

[TjerkNan]

Created new researcher account + new participant account + tested activation through feature (did not click link) and it works. Deactivation works.