Implement input for MRs over child entities

Also throwing in a proof-of-concept MR that I'd like to run in production, and then scrap once the meaty MR is finished (e.g. exploding Recurring billing events into OneTimes).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=119881471

java/com/google/domain/registry/env/common/tools/WEB-INF/web.xml

@@ -88,6 +88,12 @@
     <url-pattern>/_dr/task/resaveAllEppResources</url-pattern>
   </servlet-mapping>
 
+  <!--  Mapreduce to count recurring billing events (to test the child entity reader). -->
+  <servlet-mapping>
+    <servlet-name>tools-servlet</servlet-name>
+    <url-pattern>/_dr/task/countRecurringBillingEvents</url-pattern>
+  </servlet-mapping>
+
   <!-- This path serves up the App Engine results page for mapreduce runs. -->
   <servlet>
     <servlet-name>mapreduce</servlet-name>