Move in-process UI creation into a separate DLL.

One step further towards removing widget/GUI dependencies from the core
probe.
Remoting supported is a client/UI property, so move it there.
Extracting a reusable base class of the proxy factory.
Port the ToolFactory proxy to use the new base class.
Add proxy factory for the tool UIs.
We only need the tool UIs here, not the probe part.
All these plugins implement both the probe and the UI interface.