Trigger the Unplugged notification on app start

... rather than waiting for a device to be added or removed.

This should have been implemented as part of the Celluloid conversion, but I forgot.
I removed the relevant comment that was intended to remind me.

Fixes #57.

app/models/sensor_watch.rb

@@ -34,11 +34,7 @@ def record_race_results(_, results)
   end
 
   def handle_device_change(_)
-    if @sensor.plugged_in?
-      initialize_state
-    else
-      self.state = :unplugged
-    end
+    initialize_state
   end
 
   def start_race
@@ -58,6 +54,7 @@ def quit
 private
 
   def initialize_state
+    return self.state = :unplugged unless @sensor.plugged_in?
     if @heat.current.any?
       start_race
     else

lib/track_sensor/base.rb

@@ -83,7 +83,6 @@ def initialize_device(device_path)
 
   def scan_for_device_changes
     initialize_new_devices
-    # raise IOError.new('The sensor is not plugged in') unless plugged_in?
   end
 
   def initialize_new_devices