breaking changes.

Fixes #2955: Changed the signature of ActiveQuery constructors and `ActiveRecord::createQuery()` to simplify customizing ActiveQuery classes

fixes #2887

Refactored ActiveRecord::find() so that find(null) will also return an ActiveRecord instance instead of ActiveQuery.

so information about changed values is available in `afterSave`-event.

fixes #2892

fixed some urls in guide; moved elasticsearch png file to proper location, to be seen by apidoc generator