Update current portal level when resos are destroyed

[xosofox]

[joshka]

From dupe: As a gear starred lvl 5, I need lvl 3 resonators so that I can fully deploy on empty portals alone (2xL3, 4xL4, 2xL5). It would be nice to be able to simulate 'making' lower level portals by destroying some, but not all the opposing faction's resonators. I'd like to see the portal level recalculated based on the resonators on the portal.