Don't use any groupTemplate or generic template for hidden fields

They should just be returned as-is based on their own input template.

Say you have a form template config like this (Twitter Bootstrap comatible):

$config = [
	'formGroup' => '{{label}}<div class="col-sm-10">{{input}}{{error}}</div>',
];

Then the hidden field would also include the div in the output, even though nothing
is visible.

This will screw up the visible form quite a bit, since the div will still consume the space
horizontally, but vertically be just 0 (1?) px high.

Additionally this PR includes the `error` in both groupTemplate and label template for even more
flexibility

This is the code needed to reach quite a lot of Bootstrap compat based on this PR

$config = [
	'fieldset' => '{{content}}',

	'formGroup' => '{{label}}<div class="col-sm-10">{{input}}{{error}}</div>',

	'groupContainer' => '<div class="input {{type}}{{required}} form-group">{{content}}</div>',
	'groupContainerError' => '<div class="input {{type}}{{required}} form-group has-error">{{content}}</div>',

	'input' => '<input type="{{type}}" name="{{name}}" {{attrs}}>',
	'error' => '<div class="help-block error-message">{{content}}</div>',

	'checkboxFormGroup' => '{{label}}<div class="col-sm-10">{{input}}</div>',
];
Add test for FormHelper::input() for hidden field.
Merge pull request #3351 from cakephp/dont-use-group-template-for-hidden-fields

Don't use any groupTemplate or generic template for hidden fields