Correct most of the problems with urwid.

Now the focus gain/focus lost is handled correctly with urwid_more.
At least with the keyboard. With the mouse there still are duplicate
events. To correctly handle the focus in urwid, one must write another
library, urwid is full of dirtly hacks and shortcuts.

All in all, label validation is now ok, Lilo table is usable and most of
all, contextual help is now working good.