Add SubscriptionGraph.module() to WebAppInitializer

I689998da7 introduced a Guice binding but only hooked it up in Daemon.
We need to hook up the module in WebAppInitializer, too.

Change-Id: I8d93b8de7ac441b466bd87f8b2213c31e77f00fb
diff --git a/java/com/google/gerrit/httpd/init/WebAppInitializer.java b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
index 0c3b7b0..c5f97a3 100644
--- a/java/com/google/gerrit/httpd/init/WebAppInitializer.java
+++ b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
@@ -96,6 +96,7 @@
 import com.google.gerrit.server.ssh.NoSshModule;
 import com.google.gerrit.server.ssh.SshAddressesModule;
 import com.google.gerrit.server.submit.LocalMergeSuperSetComputation;
+import com.google.gerrit.server.submit.SubscriptionGraph;
 import com.google.gerrit.sshd.SshHostKeyModule;
 import com.google.gerrit.sshd.SshKeyCacheImpl;
 import com.google.gerrit.sshd.SshModule;
@@ -322,6 +323,7 @@
     }
 
     modules.add(new RestApiModule());
+    modules.add(new SubscriptionGraph.Module());
     modules.add(new WorkQueue.Module());
     modules.add(new GerritInstanceNameModule());
     modules.add(