[xpp_examples] Install rviz files

[mmurooka]

Thank you for the nice visualization tools. When installing via apt, *.rviz files are not found. This patch is to solve the issue.

$ dpkg -L ros-melodic-xpp-examples /. /opt /opt/ros /opt/ros/melodic /opt/ros/melodic/lib /opt/ros/melodic/lib/pkgconfig /opt/ros/melodic/lib/pkgconfig/xpp_examples.pc /opt/ros/melodic/lib/xpp_examples /opt/ros/melodic/lib/xpp_examples/monoped_publisher /opt/ros/melodic/lib/xpp_examples/quadrotor_bag_builder /opt/ros/melodic/share /opt/ros/melodic/share/xpp_examples /opt/ros/melodic/share/xpp_examples/bags /opt/ros/melodic/share/xpp_examples/bags/README.txt /opt/ros/melodic/share/xpp_examples/bags/biped.bag /opt/ros/melodic/share/xpp_examples/bags/gap.bag /opt/ros/melodic/share/xpp_examples/bags/hyq.bag /opt/ros/melodic/share/xpp_examples/bags/monoped.bag /opt/ros/melodic/share/xpp_examples/cmake /opt/ros/melodic/share/xpp_examples/cmake/xpp_examplesConfig-version.cmake /opt/ros/melodic/share/xpp_examples/cmake/xpp_examplesConfig.cmake /opt/ros/melodic/share/xpp_examples/launch /opt/ros/melodic/share/xpp_examples/launch/biped_bag.launch /opt/ros/melodic/share/xpp_examples/launch/biped_gap.launch /opt/ros/melodic/share/xpp_examples/launch/hyq_bag.launch /opt/ros/melodic/share/xpp_examples/launch/monoped_bag.launch /opt/ros/melodic/share/xpp_examples/launch/monoped_generate.launch /opt/ros/melodic/share/xpp_examples/launch/quadrotor_generate.launch /opt/ros/melodic/share/xpp_examples/package.xml /usr /usr/share /usr/share/doc /usr/share/doc/ros-melodic-xpp-examples /usr/share/doc/ros-melodic-xpp-examples/changelog.Debian.gz