Actionize the EPP endpoints.

This introduces Actions and Dagger up until FlowRunner. The changes
to the servlets are relatively simple, but the required changes to
the tests, as well as to auxillary EPP endpoints (such as the http
check api and the load test servlet) were vast. I've added some
comments in critique to make the review easier that don't really
make sense as in-code comments for the future.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124593546

java/google/registry/request/RequestParameters.java

@@ -198,5 +198,14 @@ public final class RequestParameters {
     return result;
   }
 
+  /**
+   * Returns an {@link Optional} of the first HTTP header associated with {@code name}, or empty.
+   *
+   * @param name case insensitive header name
+   */
+  public static Optional<String> extractOptionalHeader(HttpServletRequest req, String name) {
+    return Optional.fromNullable(req.getHeader(name));
+  }
+
   private RequestParameters() {}
 }