Added separator argument to getContainerClass

(default separator is ' ' when setting the class attribute, but needs to be changed to '.' when printing inline CSS).
This fixes an issue when adding both custom styles and a custom class to an area. The resulting class attribute was ok ("ccm-custom-style-area custom-class") but the inline CSS was wrong (".ccm-custom-style-area custom-class" instead of ".ccm-custom-style-area.custom-class").