Remove create admin link, Mandrill SMTP support & Roster Locking

- removed the 'create admin' link from the installation, and force user to install page from login page if no admin is found
- added support for Mandrill SMTP for all mail sends (thanks @Dimtar)
- implemented roster locking feature so admins can lock rosters and prevent teams from making changes to their league roster
- updated ezLeague version to 3.1.1

(ref https://github.com/stoopkid1/ezleague/issues/104, ref https://github.com/stoopkid1/ezleague/issues/65, ref https://github.com/stoopkid1/ezleague/issues/103)