Change transaction type

[funnym0nk3y]

I hope I did not oversee a related issue.

Is your feature request related to a problem? Please describe.
An interim funtion for #4243 and #4238 could be a manual change from withdrawal/deposit to transaction.

Describe the solution you'd like
Currently the once set transaction type cannot be changed. It would be very handy if a withdrawal transaction could be changed to transfer by the context menue. All values could be filled in automatically and source and target are added manually. That would also preserve the source comment of the importer.