Add Ability to Confirm Email Verification via API

[lizhuomeng71]

Object:
In a scenario where an APP run complete depend on Barong and Peatio API, An email verification api endpoint is missing for end to end flow.

Flow:
0. An React App is set at www.example.com interact with barong and peatio via API (feasible with current code)
0. Barong is config to use www.example.com as domain for all email (feasible with current code)

1. Customer register in react front end via post /account API (feasible with current code)
2. An Email is sent to customer inbox. with the confirmation link as https://www.example.com/accounts/confirmation?confirmation_token=dtTrFToFZ9EDuA4nxQTs (feasible with current code)
3. React App received it, sent an API call to http://barong/api/v1/accounts/confirmation?confirmation_token=dtTrFToFZ9EDuA4nxQTs (API currently not exist)
4. verification is either approved or rejected

API:
/accounts/confirmation
Param
[confirmation_token]
Response
200,
401, invalid token
422, already verified