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.

SignalStrengthSamplerTest/AndroidManifest.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+      package="com.google.android.apps.mytracks.signalstrength.test"
+      android:versionCode="1"
+      android:versionName="1.0">
+  <application android:label="Signal Strenght Sampler Test">
+    <uses-library android:name="android.test.runner" />
+  </application>
+  <uses-sdk android:minSdkVersion="3" />
+  <instrumentation android:targetPackage="com.google.android.apps.mytracks.signalstrength"
+                   android:name="android.test.InstrumentationTestRunner" />
+</manifest>