Update transaction type post-creation

Currently after creating a new transaction and saving it, it’s not possible to change the transaction type (expense, income, transfer), you can only delete the transaction and recreate it from scratch.

This can be especially problematic if you’re importing transactions from other systems and a refund or reimbursement is considered income by default and can’t be updated to be an expense with a negative number (as the guides suggest is the workflow for logging reimbursements). This will be exacerbated when automatic imports from external accounts starts happening.