`false`

variables in the form builder

This gives a lot more flexibility to the user, for instance to generate
a collection of check boxes and labels, allowing to add custom classes
or data-* attributes to the label/check_box using another object
attribute.

This basically mimics options_for_select functionality that accepts a
third option for each item to generate html attributes for each option.

[Carlos Antonio da Silva + Rafael Mendonça França]

And options_from_collection_for_select as well.

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

This will make it easy for the user to handle how check box/radio and
labels should be generated, abstracting any text/value/default html
options required to make it work.

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

* Extract value sanitization from default name and id method and new
  collection helpers;
* No need to sanitize value in default name and id always;
* Improve value_before_type_cast to avoid concating the same method name
  string twice.

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]

[Carlos Antonio da Silva + Rafael Mendonça França]