Move contactHasAddress method to RecentContactsModelPrivate

This function is only used by RecentContactsModel, and uses an enum from
that class; it does not belong in EventModelPrivate.
Move more RecentContactsModel functionality out of EventModelPrivate
Remove duplicate implementation of EventModelPrivate::fillModel

Also fixed the return value in EventModelPrivate.
Don't use GroupsUpdatedFull for ConversationModel

This was used to update events with contact info from the
GroupsUpdatedFull signal; that is redundant to and less reliable than
the contact signals we'll get anyway when contact changes are enabled.
Remove unused EventModelPrivate::findParent
Remove non-existent CallModelPrivate::resolveContact function
Return false when EventModelPrivate::executeQuery fails
Merge pull request #67 from special/eventmodel-fixes

[libcommhistory] Cleanup for EventModelPrivate and related code