[NEW] Service account directory feature

[bhardwajaditya]

• A new service Account tab is added to directory

• Search query will be searched by 3 fields - name, username and description.

• The above given three fields can be changed at any point from the settings menu

• Once a user clicks on the directory listing of the service account a direct message tab will open and the user is subscribed to service account. A new field of sa: true will be added to subscription document of the subscriber.

[kb0304]

Contains code from 6 and 7, will review after they are merged.