Fix broken links to Gazebo

Website has moved to classic.gazebosim.org.

Author: rhaschke

doc/gazebo_simulation/gazebo_simulation.rst

@@ -1,7 +1,7 @@
 Gazebo Simulation Integration
 =============================
 
-`Gazebo <http://gazebosim.org/>`_ is the most popular robotics simulator in the ROS ecosystem, so it is naturally a good fit to integrate with MoveIt.
+`Gazebo <http://classic.gazebosim.org/>`_ is the most popular robotics simulator in the ROS ecosystem, so it is naturally a good fit to integrate with MoveIt.
 
 The `MoveIt Setup Assistant <../setup_assistant/setup_assistant_tutorial.html>`_ helps setup your robot to work with Gazebo, but there are still some additional steps required to successfully run MoveIt with Gazebo.
 
@@ -49,7 +49,7 @@ For correct physical simulation of your joints, we need to add dynamics paramete
 3. Add inertia matrices and masses to the links
 -----------------------------------------------
 For correct physical simulation of your links, we need to define inertia properties for every link.
-If your robot manufacturer doesn't provide the corresponding values, you can estimate them via :code:`MeshLab` as explained in the relevant `Gazebo documentation page <http://gazebosim.org/tutorials?tut=inertia&cat=build_robot>`_.
+If your robot manufacturer doesn't provide the corresponding values, you can estimate them via :code:`MeshLab` as explained in the relevant `Gazebo documentation page <https://classic.gazebosim.org/tutorials?tut=inertia&cat=build_robot>`_.
 Add the following XML snippet to your URDF link definitions:
 
 .. code-block:: xml

doc/mesh_filter/mesh_filter_tutorial.rst

@@ -16,7 +16,7 @@ Getting Started
 
 * Clone the `Universal Robot package <https://github.com/ros-industrial/universal_robot>`_ to your workspace for Melodic. Remember to rebuild your workspace after cloning.
 
-* Install `Gazebo <http://gazebosim.org/tutorials?tut=install_ubuntu&cat=install>`_. You need to install ros-${ROS_DISTRO}-gazebo-plugins too.
+* Install `Gazebo <http://classic.gazebosim.org/tutorials?tut=install_ubuntu&cat=install>`_. You need to install ros-${ROS_DISTRO}-gazebo-plugins too.
 
 
 Running the Demo