Multiple improvements to the data hub:

* Making registration finer-grained so we only listen to the data we really need.
* Moving the system listener registration to an external class (for testability and readability)
* Adding a unit test (not yet complete)
* Adding documention and cleaning up comments

Still many things TODO:
* Allow pausing of registrations
* Add pause/resume to onPause/onResume of activities
* Move sampling logic out of the hub
* Optimize data reloading when display preferences change
* (maybe) move the data hub and related classes to the "content" package

SignalStrengthSampler/proguard.cfg

@@ -0,0 +1,34 @@
+-optimizationpasses 5
+-dontusemixedcaseclassnames
+-dontskipnonpubliclibraryclasses
+-dontpreverify
+-verbose
+-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*
+
+-keep public class * extends android.app.Activity
+-keep public class * extends android.app.Application
+-keep public class * extends android.app.Service
+-keep public class * extends android.content.BroadcastReceiver
+-keep public class * extends android.content.ContentProvider
+-keep public class com.android.vending.licensing.ILicensingService
+
+-keepclasseswithmembernames class * {
+    native <methods>;
+}
+
+-keepclasseswithmembernames class * {
+    public <init>(android.content.Context, android.util.AttributeSet);
+}
+
+-keepclasseswithmembernames class * {
+    public <init>(android.content.Context, android.util.AttributeSet, int);
+}
+
+-keepclassmembers enum * {
+    public static **[] values();
+    public static ** valueOf(java.lang.String);
+}
+
+-keep class * implements android.os.Parcelable {
+  public static final android.os.Parcelable$Creator *;
+}