SimpleMachines Forum 2.0 Support

Hello i'm create initial support for SMF 2.0.

What now imported:
- User with birthdate, email, member_name and password
- Role form membergroups
- User_Role from id_group and additional group for user. post_group not included!
- Category & Boards. Category imported as root category in vanilla forum. Hierarchy saved.
- Discussions from topic + first_message as body and subject
- Comments from messages without first_message topic

Todo:
- User avatars
- Attach to discussion & comment
- Category permissions by group
- Conversations aka Private Message