* api: Add an endpoint to list a particular member of team.

* models: Rename `GetUserTeams()` to `GetUserOrgTeams()` in `org_team` model.

`GetUserTeams()` sounds a bit misnomer since it actually returns
the teams that user belongs to in a given organization rather than
all the teams across all the organization that the user has joined.

* models: Add `GetUserTeams()`.

Returns all the teams that a user belongs to.

* api: Add an endpoint for GET '/user/teams'.

A GET request to this endpoint lists all the teams that a user
belongs to.