FIX: Ensure post has correct content-type header.
Exporting silverstripe-backend lets other modules (such as asset-admin)
use it.
In addition, the Content-type header of a post request of URL-encoded
data was being set to text/plain by default, which isn’t correct and
stopped PHP from interpreting it.
Renaming state operations from 'campaign' to 'record'.
Implemented API endpoint retrieval of GridField data.
Added more mock data into CampaignAdmin (rather than hardcoding in client),
to be replaced by CampaignAdmin API endpoint querying the real datamodel.
Using more native isomorphic-fetch instead of jQuery.ajax
to minimise dependencies and get into a more forward-thinking API.
Also catching errors in ReactJS API backend:
Emulate jQuery.ajax() behaviour. Might change at a later point
if we have a general purpose backend with a promise-based catch()
implementation.
