Redesign emails.

All emails use common functionality provided by karaage.common.emails.

Change-Id: I1731bca6dacce0feb45476c61e6f0e22b0eb1237
Rename log_object to log.

Change-Id: I0a70a236e3248cabf6a71a355106068b81f054a6
Move/simplify authenticate method.

Change-Id: I3b9aeffb2b1f38276531d4344d58ae5f1adcf854