Enhance Dynamic Subscription Email Customization

[mproy]

I think the Dynamic Subscriptions are an amazing new feature that can act as a way to push reports to users with tailored views when important changes happen in the underlying data but the lack of customization of the email that gets sent is a bit frustrating. I'd like to have a lot more options of customizing the email so it can look like a polished final product. In its current state, it really doesn't look like a clean email deliverable to the data consumers.