Export workspace as global property on ScriptEngine in QML bindings

If workspace is exported as a context property there seem to be
issues with the signals which are not bound to a property of
WorkspaceWrapper.

This problems seems to be fixable by exporting the workspace
property as a global property on the script engine.

As a side-effect this also resolves the issue with the clientList,
so we can drop the hack again.

REVIEW: 104682