* Get rid of dialog getInstance() methods and use ctors instead.
* Delete copy/assign of DialogBase rather than of every dialog.
* Make get_all_items()/sp_degroup_list() less inefficient.
* Make dialog_factory() return unique_ptr rather than reference to *new.
* Cleanup font subsitution dialog, remove class used as namespace, fix
  leaking widgets, and tweak some UI spacing to make it look nicer.