Add contact cache and pending list to ContactResolver
Remove contactCache from EventModelPrivate
WIP Disable contactCache use in RecentContactsModel, needs refactor
Set up contact listening on setResolveContacts

Before, this was inconsistently enabled after the query was executed, in
a very bug-prone way. It's cheap to enable on an empty model.
Asynchronously resolve contacts for EventModelPrivate::addToModel

To preserve the current API (for now), a synchronous option is offered
that will insert the event immediately regardless of contact resolving,
and update asynchronously if necessary. This is used only by
EventModel::addEvents, and can be removed once that function is made
asynchronous.
Port RecentContactsModel to new event contact resolution
WIP Debug and timing for contact stuff