Make InnovationsContactForm more configurable

[stevejalim]

At the moment the innovations contact form has three separate behaviours, which also involve three paths through the client-side JS. Yet, the destination list for each (and the addiitonal 'interest' list is hard-coded in both JS and Python and needs code changes to adjust.

It would be great to either:

1. make the innovations contact form block entirely CMS-configurable
   or
2. create a new contact form block that supports both newsletter signups and direct email, which could be used for Innovations and generically on any Birdbox site

[stevejalim]

cc @johnshaughnessy - I think you can see the value in this ticket :)