[Cuis] Taskbar integrated

[Juan Vuletich]

Hi Folks,

I integrated Ken's great Taskbar enhancements. I believe I fixed the 
small glitches you found.

I also did some tweaks to ExtendedClipboard package, that I moved from 
STE to main Cuis repo, so people can adopt it easily. Besides the RTF 
support, it also adds copying and pasting of graphics between Cuis and 
external apps, and even copying and pasting live morphs between Cuis 
images. It works on the Mac with the ExtendedClipboardPlugin bundled in 
the VM. For Windows we only support reading the clipboard via FFI. For 
Linux, I'm not sure, but it should just work (provided the 
ExtendedClipboardPlugin is available to the VM).

Cheers,
Juan Vuletich