New Feature: Administrator needs to activate new users

[jkmssoft]

With this new feature new registered users need to get activated after registration by an administrator before they can use their account. Example here: https://github.com/jkmssoft/yii2-user/commit/11ed33c0b5b52d385883fa0e8a1df04e83584cde

(I'm currently using my own dektrium/yii2-user fork, but there seems to be no further development. That's why I have to switch to another user/rbac extension but before I do this I have to make sure that everything is working like I need. That's why I am opening for each missing feature an issue, I hope this is ok?)

[tonydspaniard]

Thank you @jkmssoft , will add this feature request for next milestone.