Fix EZP-21095: SPI split loading user by login and email
Implement EZP-21095: API add UserService::loadByLogin

Conflicts:

	eZ/Publish/Core/Repository/UserService.php
Implement EZP-21095: API add UserService::loadByMail
Test EZP-21095: Add SignalSlot & Integration tests
Merge pull request #434 from ezsystems/loadByLogin_and_Email_EZP-21095

Implement EZP-21095: LoadUser by login and email