fixes #4012

breaking changes.

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

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

allow extending only one class to add scopes, fixes #2146

TODO:

- [ ] adjust guide docs
- [ ] adjust README files of extensions
- [ ] finish work and fix test breaks

fixes #2370

- refactored elasticsearch AR to make type and index available in
  instantiate(), issue #1313

fixes #2281

fixes #1993

meet the AR interface requirements.

now supports mapped primary key when _id is part of source with an
alias.

fixes #1469

issue #1313

Moved file and path related methods from StringHelper to FileHelper, renamed StringHelper byte methods not to be misused as string methods