AppListUpdateView: Rewrite with ListStore

[danirabbit]

Rewrites things to use a ListStore of packages which makes things like removing, sorting, adding, etc more straightforward. Separating handling data from handling UI

• Remove unused public methods
• Remove single-use methods
• Use functions from ListStore for clear and remove
• We don't need to check os_updates or runtime_updates before adding because we already do that
• Only call show_all () when the model changes.
• We already refresh the model on client.installed_apps_changed, so we don't need to also explicitly call remove from the AppinfoView