email editor 2.0 : be able to set the domain of the view as webpage token/link

Currently, when working in a multi-LP-domain environment, you can change the branding domain for the email, but the domain in which the "view as web page" is shown is always the default LP domain.

We should be able to set a different domain (one of the domains for which a domain redirect is set) for the View as Web Page links in the email. The setting should be managed at workspace level, as it's done for the branding domain, and also be modifiable in the email editor, all this being controlled by the user role.

-Greg