Show ongoing operations

[leolost2605]

Whenever a install button is clicked we add the app to the updates ListStore on the AppListUpdateView. There it shows a progressbutton with cancel ability and gets added to the installed apps list once its done as then the installed_apps_changed signal gets fired and the view updated shortly after.

Regarding the current behavior I'm not sure but I think it's wrong anyways because currently an app gets added to the update liststore only after it was installed and the installed_apps_changed signal was then already fired so that it also doesn't get removed but stays there.

To test this you might want to use a large app like GNOME Builder etc. to have enough time to switch over

Fixes #14

[leolost2605]

Ok nvm the installed_apps_changed signal doesn't get fired at all