Routing and form generation

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Hey folks, this is something I need for my special Christmas gift, kinda related to Sylius because it will make our life easier, but it should be useful for everyone. :)

This PR adds 2 things:

* Automatic form generation if it does not exist (currently supports only doctrine/orm)
* Automatic API routing generation for resources, it is currently just a simple generation and I do not want to use it in Sylius yet, because in case of Sylius we need to customize a lot of things, but wait till Monday to see what cool it can do for simpler use-cases :)

It will be improved and updated with my #2255 Resource bundle refactoring, so fear not about its current state. :P

Cheers,
Generator is used only for non-existing form types.