ClientSideWindowHandler currently only checks for an empty window.name

we currently only check for an empty window.name for detecting a new tab. But this doesn't cover the case that someone opens a new tab with target or just uses a previously copied bookmark.

All those cases can be perfectly handled by just comparing the window.name with the windowId from the URL. It if is the same then we are on the right tab. Otherwise we need to use the window.name (if not empty) or request a new windowId.