[JsonSchema] Rework Validation (part1)

[Korbeil]

Biggest current issue with validation is that Validation is done on each models one by one with no relations.
So if we have a model with a property that is another model, we won't keep the path to the validated properties in that sub-model.

The idea is to use one native Compound Constraint for each model, then to use theses constraints to validate sub-models properties.

Part 1 contains:

• Use Symfony Constraints instead of custom validators
• Make only the first Normalizer to do the validation

Part 2 will contains:

• Use theses Constraints to validate sub-models
• Add tests on sub-models validation

While we could wait for both part 1 & 2, I think part 1 is already a big step forward and considering the diff it makes, it's better to merge it now to avoid issues while rebasing.