Refactor forms support

[lulco]

Follow up #77 and #95

• create visitors (Form node visitors #182)
• use object shape (Allow final classes for custom forms #407)
• add support for containers (Added support for form fields in containers #380)
• add support for groups (Add support for groups #409, Support form groups #411)
• add support for extended classes with magic methods (added by Form extension) (Custom form methods #117)
• Collect type of Form and use it as parent of fake class in compiled template (Added type for Form collector and use it in compiled template #115)
• add Form and FormField classes (same as Variables, Components etc. are separated from CollectedVariables and CollectedComponents)
• Collect data form fields from more places and merge them together - Custom form field resolving #142
• Expression "$form" on a separate line does not do anything. (Cleanup visitor #121)
• False positive error "Form field with name "something" probably does not exist."
• Add __compilerError with Form with name *** probably does not exists when form is not found - check what errors it will return, maybe the best would be to remove whole form from begin to end and replace it with error.
• Check content of end() in form node visitor - check if formStack is there
• Collect form parts from all classes implementing some interface (Collect variables, components, form fields etc. from all classes implementing some interface #408)

private AddFieldsToFormInterface $addFieldsToForm;
...
$form = new Form();
$this->addFieldsToForm->addFields($form);

AddFieldsToFormInterface can have several implementations, we need to collect data from all of them

• If some field is conditionally added, and it is checked in latte, there should be no error