tutorial example: use Button subclass+signal instead of our own keypress methods
tutorial example: use Button subclass+signal instead of our own keypress methods

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branch : feature-sphinx

mountainstorm/urwid,douglas-larocca/urwid,drestebon/urwid,zyga/urwid,foreni-packages/urwid,inducer/urwid,drestebon/urwid,Julian/urwid,urwid/urwid,zyga/urwid,rndusr/urwid,rndusr/urwid,wardi/urwid,Julian/urwid,westurner/urwid,foreni-packages/urwid,wardi/urwid,hkoof/urwid,tonycpsu/urwid,hkoof/urwid,rndusr/urwid,inducer/urwid,foreni-packages/urwid,westurner/urwid,inducer/urwid,westurner/urwid,harlowja/urwid,drestebon/urwid,ivanov/urwid,urwid/urwid,zyga/urwid,douglas-larocca/urwid,mountainstorm/urwid,Julian/urwid,bk2204/urwid,tonycpsu/urwid,douglas-larocca/urwid,tonycpsu/urwid,mountainstorm/urwid,bk2204/urwid,urwid/urwid,hkoof/urwid,harlowja/urwid,ivanov/urwid,bk2204/urwid,ivanov/urwid,harlowja/urwid,wardi/urwid