applets/kickoff: don't load all models in root item
RecentUsageModel and ComputerModel are only used in PlacesPage, and RunnerModel is only used in SearchView, so no need to initialize those models in the root item.
RecentUsageModel and ComputerModel are only used in PlacesPage, and RunnerModel is only used in SearchView, so no need to initialize those models in the root item.