* Separate audit history interface into its own file in the overlay
package
* Add overlay.AuditHistory struct so that internalpb.AuditHistory is
only used from within the database layer
* Add overlay.GetAuditHistory function for features that will require
access to detailed audit history information
* Do not return full audit history from UpdateAuditHistory - callers to
that function only need to know the online score and whether a full
tracking period has been completed
* Move audit history tests out of satellite/satellitedb, since they are
independent of database implementation
Change-Id: I35b0c4ac23bbaabd80624f8a9631c3cb1a1f33bd
