Group and ungroup split transactions (#2805)

* Group and ungroup split transactions

* Release note

* Fix release note category

* Do not allow on reconciled transactions

* Add account validation, fix undo behavior, set split payee

* Fix lint errors

* Allow extracting some child transactions

* Disabled split/unsplit selected items menu

* Fix lint error

* Fix typecheck error

* Special Split payee

* "Split" payee on parent transaction

* Show manage payees on payee autocomplete modal

* Fix typecheck error + cleanup

* Fix typecheck error + cleanup

* VRT

* Fix tests

* VRT

* Only show split/unsplit when applicable