Release 0.7.0

This release will be a huge update of codebase and database structure. It will also include a lot of bugfixes and changes done from the release 0.6.0. Also following issues should be closed before release:

- https://github.com/dektrium/yii2-user/issues/100
- https://github.com/dektrium/yii2-user/issues/93

You can check new version by changing `yii2-user` version constraint in your composer.json to `"dektrium/yii2-user": "dev-dev"`. You are very welcome to report an issue or request a feature.

### Pre-release check-list
- [x] check for outstanding FIXME and TODO
- [x] update changelog
- [x] write a good summary of most notable changes
- [x] check for outdated documentation
- [ ] add git tag
- [ ] update demo