Do not enable Scintilla's Change History by default (#3591)

Do not enable Scintilla's Change History by default (#3591)

* It looks either a bit confusing or to have some bugs (without having
  investigated deeply, it did things I didn't understand);
* It marks all lines when reloading a file (instead of resetting to a
  blank slate);
* If marker margin is not visible, it can render the editor unreadable
  with the default settings;
* I don't see any obvious use case given its current behavior that
  warrants a so visible feature by default;
* I don't think the feature is obvious at first glance, which could
  easily lead users to wonder what that line is about.  It also looks
  similar to other editor's VCS commit status indicator (including
  git-changebar Geany plugin) display, yet behaves very differently,
  possibly increasing confusion.

So for now, I think it's better to have it disabled by default.