fixes #4086

one method for fetching data and one for sending to db.

fixes #2287

fixes #4012

fixes #3034

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

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

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

fixes #2281

fixes #1993

Fixes #1579: throw exception when the given AR relation name does not match in a case sensitive manner.
Renamed `ActiveRecord::getPopulatedRelations()` to `getRelatedRecords()`

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

- allows to have dynamic definition of attributes depended on the
  instance
- there was no real need for it to be static. Places that used it static
  have been refactored.

fixes #1318