make demos up to date 

I've updated most of the demos in `gtk/demo` so they can be compiled with the latest gtk2hs.
`.glade` files have been converted by `gtk-builder-convert` to make them compatible with gtk builders.
Despite that most of the demos in `gtk/demo` are now working, the following demos are still broken
which I have little clue about how to fix them:

*  `gtk/demo/embedded`
*  `gtk/demo/graphic`
*  `gtk/demo/treelist/ListDND.hs`

I also suggest compiling these demos automatically with the latest build, so as to remind us updaing them when major API change happens.