Add support for help text

[FlorianBoe]

Q	A
Bug?	no
New Feature?	yes
Bundle Version
Sulu Version
Browser Version

In a current project it would be helpful to add additional help text to the form fields generated by the bundle.
In Symfony Forms this functionality is already integrated and also the rendering of this information is already present in the form layout.

The information of help texts differs from classic placeholder texts (which is already present) and is characterized in particular by the fact that these just do not disappear when information is entered. Using the placeholder field therefore does not seem right to me.

[alexander-schranz]

@FlorianBoe totally make sense for me to add that. If you want to prepare a pull request for it adding a help/info field, which I think make sense to be a text_editor field. Let us know here.

The placeholder is a very good field to find where this new help/info field need also be added: https://github.com/sulu/SuluFormBundle/search?q=placeholder. I think it just need then added to the DynamicFormType so it will be added to the the fields like the Title.