[misc] Add proper methods to wait for notifications (it's important to click on the notification to dismiss it).
Improve two failing test. For ImageTest#testDefaultSelection, Selenium fails to scroll the target image into view and thus it fails to click and select it. The quick fix is to use a different image (closer to the previously selected image).
XWIKI-9240: Move the WYSIWYG editor administration section in a separate module inside xwiki-platform-wysiwyg
XWIKI-9241: Create a test module inside the WYSIWYG editor module to hold the functional tests and the page objects
* Move EditWYSIWYGTest in platform.
* Update tests after platform changes.