Fixes #802: Added support for retrieving sub-array element or child object property through `ArrayHelper::getValue()`

Renamed `attributeName` and `className` to `targetAttribute` and `targetClass` for `UniqueValidator` and `ExistValidator`.
Refactored UniqueValidator and ExistValidator.

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

also fixed count behavior according to limit and offset.
fixes #1458

fixed #1021

issue #1313

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

issue #1317