OR-496 Update the doc REST_user.md

Update the endpoint `GET /api/user/activitystreams` by adding a request
query string parameter for the domainid.
OR-496 Update the backend core

Add a parameter `domainId` for specified the community's domain
OR-496 Update backend webserver

Handle the new query string parameter
OR-496 Update and add tests
Merge pull request #341 in OR/rse from ~RPIGNOLET/rse:OR-496 to master

* commit '11164e09be9d1ada495b656c76a3a372da2726e8':
  OR-496 Update and add tests
  OR-496 Update backend webserver
  OR-496 Update the backend core
  OR-496 Update the doc REST_user.md