set Eigen PATH - ROS build

Using the same version of Eigen helps avoid memory issues.

ROS build 전 과정에서 path 설정을 해주었다.

# see below for the reason for specifying the eigen path
catkin config --init --mkdirs --extend /opt/ros/<ROS-DISTRO> --cmake-args -DCMAKE_BUILD_TYPE=Release -DEIGEN3_INCLUDE_DIR=/usr/include/eigen3
cd src

CMakelists.txt: use system Eigen
-option(GTSAM_USE_SYSTEM_EIGEN "Find and use system-installed Eigen. If 'off', use the one bundled with GTSAM" OFF)
+option(GTSAM_USE_SYSTEM_EIGEN "Find and use system-installed Eigen. If 'off', use the one bundled with GTSAM" ON)