Create RosterService, a service that provides access to
roster data on server side.

Signed-off-by: tungpham31 <tungpham31@gmail.com>
Minor refactor on MediaService.

Signed-off-by: tungpham31 <tungpham31@gmail.com>
Reformat api.js

Signed-off-by: tungpham31 <tungpham31@gmail.com>