ProjectExplorer: Introduce IDeviceFactory::iconForId()

This adds the possibility to have an icon for a device type. Now,
a Kit can have a proper icon if just the device type but not device
is selected.

Change-Id: I2a382ffd5b46cbbf74cdd0b934b3d450d300bfff
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/ios/iosdevicefactory.h

@@ -42,6 +42,7 @@ public:
 
     QString displayNameForId(Core::Id type) const override;
     QList<Core::Id> availableCreationIds() const override;
+    QIcon iconForId(Core::Id type) const override;
 
     bool canCreate() const override;
     ProjectExplorer::IDevice::Ptr create(Core::Id id) const override;