dataprovider: add support for user status and expiration

an user can now be disabled or expired.

If you are using an SQL database as dataprovider please remember to
execute the sql update script inside "sql" folder.

Fixes #57

httpd/api_utils.go

@@ -350,5 +350,11 @@ func compareEqualsUserFields(expected dataprovider.User, actual dataprovider.Use
 	if expected.DownloadBandwidth != actual.DownloadBandwidth {
 		return errors.New("DownloadBandwidth mismatch")
 	}
+	if expected.Status != actual.Status {
+		return errors.New("Status mismatch")
+	}
+	if expected.ExpirationDate != actual.ExpirationDate {
+		return errors.New("ExpirationDate mismatch")
+	}
 	return nil
 }