Add user administration

Hi,
I want to setup a self-hosted instance for a closed group of users. My current solution would be to hide it behind Basic-Auth but allowed users can still create random Accounts. Therefore I need an user administration, meaning only the admin can manage the users
- create new users; this can include the social-auth methods (e.g. confirm account).
- delete users
- block users (only disable login)
- no guest mode (#237)

Optional features could be
- custom names (independent of email-address/social-name) (#268)
- user management with LDAP / PAM (#93)
- store social-credentials in LDAP (Network, Username, ...)
- use login credentials from Basic-Auth