fix RecentModel ordering

UsageStatistics::update() was being called before setLastUsed()
in the ContactMethod which resulted in the lastUsedChanged signal
not being emitted and so the RecentModel was not being re-ordered.

Change-Id: I866b213ae97aacd5bd6ef6157fb136a436952b08
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>