First step of data flow refactoring.

This moves all data source connections into the TrackDataHub.

There are still many things to (re)do here:
- Optimizations about when the listeners are registered
- Optimizations about what data each TrackDataListener is interested in
- When activities are restarting, send new data since they were stopped (instead of doing a full reload)
- Proper double-buffering of Location objects (some listeners are interested in double-buffering all points, while others are only interested in double-buffering sampled points)
- etc.

MyTracks/res/menu/main.xml

@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+  <item android:id="@+id/menu_start_recording"
+    android:icon="@drawable/ic_menu_recordtrack"
+    android:title="@string/start_recording"/>
+
+  <item android:id="@+id/menu_stop_recording"
+    android:icon="@drawable/ic_menu_stoprecording"
+    android:title="@string/stop_recording"/>
+
+  <item android:id="@+id/menu_list_tracks"
+    android:icon="@drawable/ic_menu_tracklist"
+    android:title="@string/list_tracks"/>
+
+  <item android:id="@+id/menu_list_markers"
+    android:icon="@drawable/ic_menu_waypoints"
+    android:title="@string/list_markers"/>
+
+  <item android:id="@+id/menu_settings"
+    android:icon="@android:drawable/ic_menu_preferences"
+    android:orderInCategory="1001"
+    android:title="@string/settings"/>
+    
+  <item android:id="@+id/menu_aggregated_stats"
+    android:orderInCategory="1002"
+    android:title="@string/aggregated_stats"/>
+
+  <item android:id="@+id/menu_sensor_state"
+    android:icon="@drawable/ic_menu_sensorstatus"
+    android:orderInCategory="1000"
+    android:title="@string/sensor_state"/>
+    
+  <item android:id="@+id/menu_help"
+    android:icon="@android:drawable/ic_menu_info_details"
+    android:orderInCategory="1003"
+    android:title="@string/help"/>
+
+</menu>