Allow admin/editors to upload a default user profile image (journal-specific)

[pgoussy]

Is your feature request related to a problem? Please describe. TIA has requested the ability to set a custom journal-specific default profile thumbnail to display on the Editorial Team page (for those editors who haven't uploaded a headshot yet)

Describe the solution you'd like It seems like the easiest option would be to add a new Default Profile Image option to the Image Settings page, and populate that image to all user accounts that haven't uploaded a custom image.