Add Context.getSystemService(Class<?>).

Added an overload of getSystemService() that takes a class instead of a
service name to eliminate the extra cast and provide more type safety.

Cleaned up docs.

Removed the default constructor of BatteryManager which should not have
existed.

Change-Id: I9da46b20641fc83ecd3342560e5b94cb721f289c
diff --git a/api/removed.txt b/api/removed.txt
index 9322973..8668a77 100644
--- a/api/removed.txt
+++ b/api/removed.txt
@@ -16,6 +16,10 @@
 
 package android.os {
 
+  public class BatteryManager {
+    ctor public BatteryManager();
+  }
+
   public final class PowerManager {
     method public void goToSleep(long);
     method public deprecated void userActivity(long, boolean);