[Validator] improved image validator

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | symfony/symfony-docs#2840

CHANGELOG
* Added options to validate image aspect ratio (`minRatio` and `maxRatio`)
* Added options to validate if the image ratio is square, landscape or portrait (`allowSquare`, `allowLandscape`, and `allowPortrait`)