Massaged the changes

- Restored binary compatibility. The draft API has changed in some
  significant way when it became public, and the PR took the liberty to
  delete removed constants and method signatures. I brought them back so
  that older clients can keep functioning.

- Introduced a builder pattern to create PR review

- replying to a review comment should be an instance method, not a
  static method.

- GHPullRequestReview and GHPullRequestReviewDraft was not making sense
  to me, since GitHub API doesn't differentiate them. It creates a
  practical problem of not being able to submit a review comment unless
  you created the review comment in the same JVM session. That said, I
  don't understand the point of this two phase approach in the GitHub
  API to begin with!

src/test/java/org/kohsuke/github/PullRequestTest.java

@@ -7,8 +7,7 @@ import java.io.IOException;
 import java.util.Collection;
 import java.util.List;
 
-import static org.hamcrest.CoreMatchers.is;
-import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.CoreMatchers.*;
 
 /**
  * @author Kohsuke Kawaguchi
@@ -33,9 +32,10 @@ public class PullRequestTest extends AbstractGitHubApiTestBase {
     public void testPullRequestReviews() throws Exception {
         String name = rnd.next();
         GHPullRequest p = getRepository().createPullRequest(name, "stable", "master", "## test");
-        GHPullRequestReviewDraft draftReview = p.newDraftReview(null, "Some draft review",
-                GHPullRequestReviewComment.draft("Some niggle", "changelog.html", 1)
-        );
+        GHPullRequestReview draftReview = p.createReview()
+            .body("Some draft review")
+            .comment("Some niggle", "changelog.html", 1)
+            .create();
         assertThat(draftReview.getState(), is(GHPullRequestReviewState.PENDING));
         assertThat(draftReview.getBody(), is("Some draft review"));
         assertThat(draftReview.getCommitId(), notNullValue());
@@ -50,9 +50,10 @@ public class PullRequestTest extends AbstractGitHubApiTestBase {
         assertEquals(1, comments.size());
         GHPullRequestReviewComment comment = comments.get(0);
         assertEquals("Some niggle", comment.getBody());
-        draftReview = p.newDraftReview(null, "Some new review",
-                GHPullRequestReviewComment.draft("Some niggle", "changelog.html", 1)
-        );
+        draftReview = p.createReview()
+            .body("Some new review")
+            .comment("Some niggle", "changelog.html", 1)
+            .create();
         draftReview.delete();
     }