Display full name (#20171)

The setting `DEFAULT_SHOW_FULL_NAME` promises to use the user's full name everywhere it can be used.

Unfortunately the function `*user_model.User.ShortName()` currently uses the `.Name` instead - but this should also use the `.FullName()`.

Therefore we should make `*user_model.User.ShortName()` base its pre-shortened name on the `.FullName()` function.

models/user/user.go

@@ -485,6 +485,9 @@ func (u *User) GitName() string {
 
 // ShortName ellipses username to length
 func (u *User) ShortName(length int) string {
+	if setting.UI.DefaultShowFullName && len(u.FullName) > 0 {
+		return base.EllipsisString(u.FullName, length)
+	}
 	return base.EllipsisString(u.Name, length)
 }