Add className to FormComponentLoader

[EloyID]

Is your feature request related to a problem? Please describe.
When I want to use inputClassname with a formcomponent that has to query the options, the FormComponentLoader wraps the element with inputClassname and, e.g., the halfWidthLeft has no effect
https://github.com/VulcanJS/Vulcan/blob/devel/packages/vulcan-forms/lib/components/FormComponentLoader.jsx

Describe the solution you'd like
I would like to add an option formLoaderClassname to be passed to the FormComponentLoader similare to inputClassname to FormComponentInner
https://github.com/VulcanJS/Vulcan/blob/devel/packages/vulcan-ui-material/lib/components/forms/FormComponentInner.jsx

Describe alternatives you've considered
I tried to use classnames to make it work, but the object classes is not passed to the FormComponentLoader and I don't know how to make it work