[feature request] ask to merge parties/debts when trying to rename to an existing entry

[bockulator]

In the "Parties / Debts" menu say there are two parties "www.amazon.com" and "amazon". When attempting to rename a party, say "www.amazon.com" to "amazon", a toast is displayed indicating that the party "amazon" already exists.

I'd suggest opening the "merge parties" dialog instead, or adding an action to the toast for the option to open the "merge parties" dialog.