add a script that add a frame on imu
Move python node to script/
Add rospy dependencies to the package
Add a python node to log acc from imu topic
Wait for ROS clock time on RT-SLAM init

Needed later when we're going to initialize camera and robot poses
from tf when online

NodeHandler added to main to initialize ROS before rtslam init
When online, initialize camera pose from tf
Get slam_origin from tf on init func and broadcast it from main func

The rtslam/origin frame is where the robot is in the begining of the
estimation. The estimated transforms are broadcasted as rtslam/estim
frame and have rtslam/origin as parent frame.

While here, timestamp the broadcasted frames with the date of the
image
Rotate the IMU data in 180 degrees on x-axis

The IMU frame on liu-quads is FRD (Front-Right-Down), while the robot
frame is FLU (Front-Left-Up).

Maybe we should add a imu_frame on tf later, so we would be able to
translate it easily later.