Add user timezone to user create parameter

[martinrm77]

Problem description

All new users are created with timezone UTC. It is very inconvenient to make all users edit their time-zone after first logging in.
It is preferable to have an option for setting the new user time-zone or maybe also take it from a header.

Steps to reproduce the problem

1. Log in with user with graylog-plugin-auth-sso
2. Check your user timezone by checking your user profile

Environment

• Graylog Version: 2.1.2
• Plugin Version: 1.0.3
• Elasticsearch Version:
• MongoDB Version: 3.2
• Operating System: RHEL 7.3
• Browser version: Firefox 50