implement FPS-like draw-per-Xmsec. pattern. Still not very efficient.
implemented single surface for all keyboards and parameter blocks.

It was a bad idea. Very inefficient.
Add hacky project icon.
avoid local double buffering by overwriting buffer image on another buffer, which is not very efficient.

I now tried automatic double buffering in GtkBackend, but even with that
the drawing performance is not great... maybe Xwt itself is too heavy to deal
with a lot of operations.
OK, it was Font that caused significant performance loss. Reuse them without calculating it every time.
update xwt that enabled Gtk double buffering.