Embed form-designer in event and contribution UIs

I spent a couple hours trying and encountered a few issues. The unaddressed issues are:

1. "Event" - Allows an arbitrary number of profiles and provides JS for add/remove functionality. How do we want this to work "ProfileSelector"'s create/edit/preview?

2. "Event" - The rules on what CustomGroups are visible are more complex than the rules for activities or contributions. Need more advanced filtering.

3. "Contribution Page": Need to determine contribution_type_id and send to client

4. "Contribution Page": Need to determine whether the contribution-page processes memberships; if so, which "Membership" CustomGroups go on the palette? (I think we need to show all of them since one form can support multiple membership types based on end-user selection.)

5. The old behavior is to allow one to choose profiles of type (Individual,Contact,Contribution) or (Individual,Contact,Membership). The ProfileSelector widget currently uses a simplification – it expects that all profiles in the list support the same entities. (The form-designer is flexible about entities, but we have some fudgy bits to ensure this works with the existing form-runtime.) There are a couple ways to deal with this – probably merits "sleeping on it" and a tcon.

Most of these issues can probably be done within the "1-2 day" estimate. The last one I'm not sure about.