#130 - Migrated action_view_extension to Rails 4.
* ActionView::Helpers::InstanceTag is not available in Rails 4. I've used ActionView::Helpers::Tags::Base in it's place. ActionView::Helpers::Tags::TextField & ActionView::Helpers::Tags::CheckBox (in the spec) have been used for creating textbox and checkbox respectively.
* The field 'drop_hidden_field' is no longer available. Instead 'include_hidden' field is used in the new Rails. The classes that used drop_hidden_field for checkbox have already been migrated to use include_hidden field.
* The DEFAULT_FIELD_OPTIONS in InstanceTag specified the field size to be 30. Have to specify that explicitly as this is no longer available. Moreover the to_check_box_tag method is no longer available. As a side effect the alias 'alias_method_chain :to_check_box_tag, :optional_hidden_field' has to be removed.