Allow to use GWTORM Key classes in plugins

To implement dedicated databases in plugin based on GWTORM, keys are
needed. Currently they can only be used from classes located in the
same package.  Changing the modifiers to public allow the plugin to
reuse them, without keep using the same package name as in Gerrit core.

Change-Id: I5f321aa89dbb9b71945c4bc53151e3d5a26cce74

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java

@@ -106,7 +106,7 @@ public final class Change {
     private static final long serialVersionUID = 1L;
 
     @Column(id = 1)
-    protected int id;
+    public int id;
 
     protected Id() {
     }

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/LabelId.java

@@ -23,9 +23,9 @@ public class LabelId extends StringKey<com.google.gwtorm.client.Key<?>> {
   public static final LabelId SUBMIT = new LabelId("SUBM");
 
   @Column(id = 1)
-  protected String id;
+  public String id;
 
-  protected LabelId() {
+  public LabelId() {
   }
 
   public LabelId(final String n) {

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/PatchSet.java

@@ -32,12 +32,12 @@ public final class PatchSet {
     private static final long serialVersionUID = 1L;
 
     @Column(id = 1)
-    protected Change.Id changeId;
+    public Change.Id changeId;
 
     @Column(id = 2)
-    protected int patchSetId;
+    public int patchSetId;
 
-    protected Id() {
+    public Id() {
       changeId = new Change.Id();
     }