rename 'Stylepicker4ward' to 'MetaModelsPicker' see #318

There is a language var missing? -> `$GLOBALS['TL_LANG']['MSC']['metamodelspicker_noItems']` and `$GLOBALS['TL_LANG']['MSC']['metamodelspicker']`

Which text schould be placed in there?
This is missing in the language file, isn't it (it even was before)? :)
Would be nice if you could add it.