API CHANGE. customer find now takes a hash

to allow flexibility to search by customer id or email
cream#find now allows searching by email
on registering and customer exists in CRM...

if they have the same email address associate the records
previous implementation would create a new CRM record instead
tidy up
Merge pull request #650 from moneyadviceservice/3576-existing-crm-customers

3576 existing crm customers