Docs: Correction to alarm-firing frequency info, restoration of "training nav".

Corrected alarm-firing info to reflect that alarms don't fire more than
once per 15 minutes in Doze. Also, the "Previous   Next" had gone away from
the top-right nav box. This CL also fixes that regression.

Change-Id: Ied35284dd14a926adce8847beb039513ffc370f3