Nexus: Clean up supplicant events, protocol, and continue plumbing

    - Create SupplicantEvent classes for events
    - New SupplicantEventFactory for creating events
    - Extract Controller -> NetworkManager callbacks into IControllerHandler
    - Move ScanResult handling from Supplicant -> WifiController
    - Plumb more 'onConnected()' code
    - Instead of re-creating NetworkList every-time, merge in
      new entries
    - Extract SupplicantListener -> Supplicant callbacks into
      ISupplicantEventHandler
    - Move SupplicantListener callback handling to WifiController
    - Add unlocked version of lookupNetwork()
    - Save supplicant config after setting a WifiNetwork variable
    - Move property registration from WifiNetwork -> Supplicant
    - Change wifi enable broadcast messages
    - Add 3 new events: 'onAssociating', 'onAssociated', 'onConnectionTimeout'
    - Add support for handling KeyManagement

Signed-off-by: San Mehat <san@google.com>