Replaced ComponentErrorHandler with generic ErrorHandler (#10231)

Replaced ComponentErrorHandler with generic ErrorHandler (#10231)

* Replaced AbstractComponent ErrorHandler with ClientConnector level error handler. Now uses the same ErrorHandler as other parts of the framework.
* Made error handling hierarchical so that the error handler of the connector where the error occured or its ancestors is used. Falls back to VaadinSession ErrorHandler.
* Changed ErrorEvent to be a class as all other events in the framework
* Renamed ErrorListener to ErrorHandler and DefaultErrorListener to DefaultErrorHandler for consistency
* Unified error handling in AbstractCommunicationManager
* Unified error handling in VaadinServlet and VaadinPortlet
* Removed superfluous ErrorEvent implementations (#10232)

Change-Id: Ied518e05209fe54685f4bebab0709b1cd5584fd1