Add the generation of Models, migrations and model factories

[Jhnbrn90]

In this PR I've added the ability to generate model classes, migration classes and model factory classes. The models can be generated with or without accompanying migrations and/or model factories.

The classes can be generated as described in the updated readme.

To create a migration and a factory together with a model, users can attach the -m or -f flags (like in a Laravel application) or use the fully specified flags --migration or --factory.

./vendor/bin/pkg-tools make:model ExampleModel -mf

Let me know if there are some things up for improvement.