- Fix `callable_mp` bindings to methods which used to have default
arguments passed to `bind_method`. We now have to re-specify them
manually when connecting.
- Re-add `GroupsEditor::update_tree` binding.
- Misc code quality changes along the way.
Remove now unnecessary bindings of signal callbacks in the public API.
There might be some false positives that need rebinding if they were
meant to be public.
No regular expressions were harmed in the making of this commit.
(Nah, just kidding.)
