Add additional class names and style to components and error indicators to distinguish different error levels.
Vaadin 8 implementation of #9816. Cherry picked changes and added compatibility package component changes and tests.
Resolves #3139
Refactor Html5 DnD feature based on API review (#9306)
* Refactor Html5 DnD client side based on API review
- Moved classes to "correct" packages.
- Removed method DragSourceExtension.clearDataTransferText()
- Remove ButtonDragSource in favor of more generic API