replace SwXTextSectionClient with Impl struct, use UnoImplPtr to lock dtor.
move all implementation details out of header, into Impl struct.
remove ugly destruction of SwUnoCrsr via Application::PostUserEvent.
replace broken SwClient iteration with a WeakReference in SwSectionFmt.
add factory function CreateXTextSection.
use new XUnoTunnel and XServiceInfo helpers.
clean up the implementation a little.