Replace multiple factories with one factory

[neomerx]

The package uses multiple factories for its components. If replaced with one factory it will simplify package extensions.

[neomerx]

People who use #40 should be notified with this update

[neomerx]

Shortly

• instead of extending multiple factories developers should extend \Neomerx\JsonApi\Factories\Factory
• method Encoder::getFactories was replaced with Encoder::getFactory and should return FactoryInterface (which is extension for all factory interfaces in the package)