Move to rx3 package to allow side-by-side usage with RxJava 2.

Author: greenrobot-team

objectbox-rxjava3/src/main/java/io/objectbox/rx/RxBoxStore.java renamed to objectbox-rxjava3/src/main/java/io/objectbox/rx3/RxBoxStore.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package io.objectbox.rx;
+package io.objectbox.rx3;
 
 import io.objectbox.BoxStore;
 import io.objectbox.reactive.DataSubscription;

objectbox-rxjava3/src/main/java/io/objectbox/rx/RxQuery.java renamed to objectbox-rxjava3/src/main/java/io/objectbox/rx3/RxQuery.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package io.objectbox.rx;
+package io.objectbox.rx3;
 
 import java.util.List;
 

objectbox-rxjava3/src/test/java/io/objectbox/rx/QueryObserverTest.java renamed to objectbox-rxjava3/src/test/java/io/objectbox/rx3/QueryObserverTest.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package io.objectbox.rx;
+package io.objectbox.rx3;
 
 import org.junit.Before;
 import org.junit.Test;