* Replace raw pointers/new/delete with std::unique_ptr.
* …NOT including SPDesktop deleting Canvas*Group @ dtor, which crashes…?
* Replace public desktop, window, etc. pointers – with getters+setters.
* Prefix those pointers w/ _ per coding style plus existing member vars.
* Rename event_context & getEventContext() to tool & getTool() per revw.
* Drop the infernal unneeded `dtw->` (copy of `this`) prefix where diff.
* Remove unused (never populated) _connections and loop disconnect()ing.
* Remove unused, always-false result from showInfoDialog() functions.
* In inkscape-window, use make_managed(), instead of `new` and manage();
* and avoid therein an unnecessary (tautological) dynamic_cast<>() call.
* Use auto_connection instead of disconnect()ing in destructors.
* Avoid raw `new` and `delete`, possible leaks in desktop.* w/ UPtr too.
* Avoid unnecessary use of sigc::ptr_fun when can just use function ptr.
* Bin pointless setting o...