JSLint fixes.
CKEDITOR.style#apply/remove's argument should be editor instance not document.
Grouped methods augmenting editor in one place.
Documentation improvements and code style fixes.
Implemented basic custom style handlers registering.
Implemented styleHandler.setup.
Added editor instance to required arguments of style instance methods.
Pass editor instance to style's methods in every place where we can use custom style.
Implemented widget styles handler.
Implemented widget's methods for handlig classes and styles.
Added samples for styling widgets.
Set default assignedTo property of a custom style if not specified.
Made stylescombo using assignedTo property of style.
Implemented simple buildPreview.
Ordered styles used in the sample in more reasonable order.
Use data.classes to store classes applied to widget.
Inline sample doesn't make sense without contents styles.
Added support for style.toAllowedContentRules method.
Introduced widgetDef.styleableElements and widgetDef.styleToAllowedContentRules.
Added mathjax to the widget styles sample.