Form options defined as required should be supported too

[stof]

Currently, the option completion seems to support only options defined with a default value.

It would be great to support required and optional options:

$resolver->setRequired(array('first_required', 'other_required'));

$resolver->setOptional(array('optional_setting'));
// OptionsResolver::setOptional is deprecated in Symfony 2.7. It is replaced by isDefined
$resolver->setDefined(array('optional_setting'));

all these methods accept both a string or an array of strings as argument

[Haehnchen]

navigation missing for now, but completion is working