Store destination branch in notedb

This adds a 'Branch' footer to the commit message of the
refs/changes/XX/YYYY/meta notes branch when the change is created.

Tests which manually insert new changes must be adapted to make an
initial commit to the notes branch which contains the branch info.

Change-Id: If6ffadf722ca5c48e159889aedbc1ffba27a8d5a
Signed-off-by: Edwin Kempin <ekempin@google.com>

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

@@ -551,6 +551,10 @@ public final class Change {
     return dest;
   }
 
+  public void setDest(Branch.NameKey dest) {
+    this.dest = dest;
+  }
+
   public Project.NameKey getProject() {
     return dest.getParentKey();
   }