Add avatar API call

[bernalrs]

Would be nice to add the get avatar API call to this project.

Get avatar for user  GET /rest/usermanagement/1/user/avatar

Returns the url of the user's avatar

Request

query parameters

parameter	type	description
username	string	the name of the user
s	int Default: 128	the requested avatar size in pixels

Responses

• Status 303
  the uri for the user's avatar (in the location header)

• Status 404
  the user doesn't exist, or doesn't have an avatar defined