dabbrev should use QCompleter

dabbrev should use QCompleter if c.config.getBool('use_qcompleter'), not the tab completer, which requires more typing and doesn't allow completion selection using cursor keys.

doing

  w = self.c.frame.body.bodyCtrl.widget
  qcompleter = w.init_completer(aList)

instead of

  self.dynamicExpandHelper(event,prefix,aList,w)

in LeoPyRef.leo#Code-->Core classes-->@file leoEditCommands.py-->abbrevCommandsClass-->dynamic abbreviation...-->dynamicExpansion M-/

is almost enough, the completer is posted and works with cursor keys, but typing additional letters doesn't refine the completion.