EZP-20948: refactored BinaryFile URI & ID handling

- renamed path to id
- added uri property

Tests updated and passing
EZP-20948: Fixed IOService + tests after refactoring
EZP-20948: Fixed handlers tests
EZP-20948: Fixed IOLegacy handler + tests
EZP-20948: Fixed ImageStorage return value for null case

Was generating a notice in Legacy\Converter\Image

true would
EZP-20948: Added BC layer for id -> path
EZP-209498: added BC doc entry
EZP-20948: added parent:: calls for __set & __get
EZP-20948: Fixed after rebasing from master