Can't add user to a specific repo or team

[thibaultmeyer]

When we try to assign user to a specific project or a team, we get the error user does not exist..

[Bwko]

This is caused by commit 55bd3ed
It is caused by:

 -	UserName  string `json:"username"`
 +	UserName  string `json:"login"`

[lunny]

This have been resolved by #362