Keep the ridden aircraft's layer when Contacts ends, and clear its rows from Live Signals

Riding an aircraft now adopts its layer the way a direct selection does, and
Contacts gives up a dependency the user adopts, so ending Contacts mid-session
(one of its layers off, or Contacts itself) no longer turns off the ridden
layer and ends the Cockpit. When Contacts goes off, Live Signals drops the
rows built from its snapshot instead of leaving stale distances marked
CURRENT, and the feed-off warning is no longer duplicated.

src/layers/awareness/controls.js

@@ -23,6 +23,7 @@ export function createControls({ state: layerState, services, parts, source }) {
 
     attachDataManager(dataManager) {
       layerState.dataManager = dataManager;
+      parts.dependencies.watchAdoptions(dataManager);
     },
 
     setParams(params = {}) {