Xwt.Wpf: enable propagation of Key-Events in ScrollViewBackend
rename DeviceComposer => BackendComposer
TESTCODE, try to revert this: Xwt: propagating key-events -
introduce SwfDesktopBackend in  SwfEngine | clean out explizit usage of GdiEngine
cleanups
XwtBackend.DisplayBackend: introduce keyevents
Prototyping inplace-editing in canvas