revised default function key macros

 * use shorter function key macros.
 * instead, every function key has a commandline editing macro
   based on the macro "^Tc"
 * dot is no longer modified to calculate positions, instead
   Scintilla messages are used
 * prevent that function key macros move dot off-page
 * improved behaviour: HOME will will first skip spaces and tabs at the
   beginning of the line and only the second press will move dot to
   the real line beginning.
   UP and DOWN will try to keep the column. However this does not
   work quite as good as in other editors, since there's no (sane) way to
   save the column last set by one of the function keys.