Prevent reloads of new contribution, event registration, new membership, new relationship forms by Implementing dojo method to add custom fields to the form

Currently these forms reload when a "type" is selected - to allow us to retrieve and inject additional custom fields into the form based on the object type (e.g. a Participant with participant role of "Speaker" may have a set of custom fields associated with that type). The New Event Registration form reloads twice (once when Event is selected, and again when Participant Role is selected)
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These reloads are confusing, slow down data entry and may cause loss of data entered in a field while page is reloading.

The new model should retrieve additional fields / properties via ajax w/o reloading the entire page.

Implement this interface for all the places, where we use custom data and reload the page.