… added show-line-numbers and indent-unit
preferences dialog auto saves :input fields as cookies by the field
preferences dialog, on saving line numbers pref, updates code editors:
ui -> editor pool -> editors
preferences dialog shows/hides but does not rebuild each time anymore
NOTE: all editor types return "this" from constructor not just DIV
element anymore, and to preserve backwards-compatibility, sets the root
DIV as 'this.element'