[User Accounts] Watchlist API

[the-real-chrizzo]

As a user
I want to be able to store my watchlist data in the cloud
to have the data available on different devices

Background
This story entails the storage of the data in our database and providing it to the web client.
Data is not needed to be encrypted.

Acceptance criteria

API is implemented
API is agreed on with the web team
Data is written in the database
API should allow bulk deletions or additions to happen
SDK will provide the functions implemented here