Minor improvements in handling offline applications

Summary:
Some minor loose ends from exploratory testing:

- disconnect device logs event listeners if the device disconnects
- show metro if that is still up, even if the app is no longer connected
- hide the options in the support form to record videos / screenshots if the device isn't connected

Reviewed By: nikoant

Differential Revision: D26277100

fbshipit-source-id: 49d0c934d587b226bc25524224efce60b53939e9

desktop/app/src/devices/BaseDevice.tsx

@@ -225,6 +225,7 @@ export default class BaseDevice {
   }
 
   disconnect() {
+    this.logListeners.clear();
     this.connected.set(false);
   }