Add assetic to our Symfony instance.
Rewrite step2 install JavaScript with assetic.

All id's have been rewritten to the Symfony versions, JavaScript uses
assetic and has been cleaned up a little.
Add a submit button.
Save the data from step 2 in the session.
Add the Form on the thirth step.

Note: it uses a kinda strange hack to make sure the required modules are
checked and disabled. I couldn't find a cleaner way to achieve this
result.
Cleanup.
Make sure the required modules are always selected.
Lower complexity.
Save the data from the modules form in the session.
Add the databases form on step 4.
Add the default port.
Calculate default values for the database data.

Since we're not working with entities, we can't set default data in a
normal way. Using an event listener on the formBuilder, we can
manipulate the data right before it gets inserted in the form.

I haven't decided yet if we should use an object containing all
installation data instead off the parameterBag in the session.
Validate the database credentials.

Note: this is done with SpoonDatabase now, but this should be replaced
by something more Symfony later (like doctrine).
Display form errors on all steps.
Refactor form theme to an external file.
Save the settings from the database step.
Add the login information form.
Create an installer service that will install Fork.

It is based on an array (because off reusability in commands,...). For
now, it just validates the inserted data.
Install the Fork Core From the installer service.
Fetch warnings and defaultExtras from the CoreInstaller.