Update fingerprint settings to spec

- Make it look like a sub settings activity, with back button
- Add disclaimer to describe what your fingerprint can be used for
- Update visuals and text for "Add fingerprint"
- Update related string

Bug: 20594955
Change-Id: I0adfcc743db386e0abf9cfdafff3d068ebc3b4bc

src/com/android/settings/HelpUtils.java

@@ -118,7 +118,7 @@ public class HelpUtils {
         }
     }
 
-    private static Intent getHelpIntent(Context context, String helpUriString) {
+    public static Intent getHelpIntent(Context context, String helpUriString) {
         // Try to handle as Intent Uri, otherwise just treat as Uri.
         try {
             return Intent.parseUri(helpUriString,