Setup Mailer: sender name and e-mail fields

Currently, the Setup Mailer step doesn’t contain the sender name and e-mail fields:

Instead, this is done on the Send Mail step:

I suggest adding the possibility to setup a default sender name and e-mail during Setup Mailer, so if we need to change this we can do so without going through all the Send Mail steps around our app. The fields on Send Mail, if defined, would override the default ones set in Setup Mailer.

Edit: The implementation of this feature would require a deeper change in the UI: validation for empty sender fields on the Send Email step would need to check the Setup Mailer step to see if those values are present before giving an error message for empty sender fields